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Adaptation of Spirogyra insignis (Chlorophyta) to an extreme natural environment (sulphureous waters) through preselective mutations
New Phytologist
Abstract
Adaptation of Spirogyra insignis (Chlorophyceae) to growth and survival in an extreme natural environment (sulphureous waters from La Hedionda Spa, S. Spain) was analysed by using an experimental model. Photosynthesis and growth of the alga were inhibited when it was cultured in La Hedionda Spa waters (LHW), but after further incubation for several weeks, the culture survived due to the growth of a variant that was resistant to LHW. A Luria-Delbruck fluctuation analysis was carried out to distinguish between resistant filaments arising from rare spontaneous mutations and resistant filaments arising from other mechanisms of adaptation. It was demonstrated that the resistant filaments arose randomly by rare spontaneous mutations before the addition of LHW (preselective mutations). The rate of spontaneous mutation from sensitivity to resistance was 2.7 x 10(-7) mutants per cell division. Since LHW(resistant) mutants have a diminished growth rate, they are maintained in nonsulphureous natural waters as the result of a balance between new resistants arising from spontaneous mutation and resistants eliminated by natural selection. Thus, recurrence of rare spontaneous preselective mutations ensures the survival of the alga in sulphureous waters.
Supplementary resource (1)
Data
November 1998
... La Hedionda is a sulfide-rich (200 µM) thermal (20 • C) spring outflow in southern Spain [1,2] ( Figure 1). While the sulfide-rich water of La Hedionda has been appreciated in thermal baths since almost 61 before Christ [3,4], sulfide is also a biocide because it blocks photosystem II (PSII) and respiratory electron transport [5][6][7][8][9]. However, cyanobacteria strains inhabiting sulfureous habitats with sulfide as an electron donor to PSI [11,[13][14][15][16]. ...
... For this reason, we initially addressed the study of the adaptation processes of cyanobacteria to La Hedionda water [2] and, in this study, we hypothesized that the levels of sulfide in this habitat could be the main trigger of cyanobacteria populations. However, despite the fact that sulfide-rich spas are natural laboratories for studying eco-evolutionary processes involved in the adaptation of photosynthetic organisms to sulfide [2,4,17,18], little information exists about the seasonal variability of the sulfide concentration and low diversity populations of photosynthetic organisms inhabiting these extreme ecosystems [4]. It must be highlighted that the usual phytoplankton succession has been widely studied in epicontinental waters where annual cycles depend on physical control, nutrients and grazing [19]. ...
... For this reason, we initially addressed the study of the adaptation processes of cyanobacteria to La Hedionda water [2] and, in this study, we hypothesized that the levels of sulfide in this habitat could be the main trigger of cyanobacteria populations. However, despite the fact that sulfide-rich spas are natural laboratories for studying eco-evolutionary processes involved in the adaptation of photosynthetic organisms to sulfide [2,4,17,18], little information exists about the seasonal variability of the sulfide concentration and low diversity populations of photosynthetic organisms inhabiting these extreme ecosystems [4]. It must be highlighted that the usual phytoplankton succession has been widely studied in epicontinental waters where annual cycles depend on physical control, nutrients and grazing [19]. ...
A seasonal cycle of sulfide, nitrate, phosphate, ammonium, chlorophyll a (Chl a) and Oscillatoria sp. abundance (<100 μm), as well as the relative contribution of taxonomic phytoplanktonic groups (cyanobacteria, green algae, cryptomonads, diatoms and dinoflagellates) to total Chl a were measured by fluorometric measurements at La Hedionda sulfide-rich spa (southern Spain). Fluorometry determined that cyanobacteria Chl a concentration correlated positively with the abundance of Oscillatoria sp. Aggregates at 45–100 μm equivalent spherical diameter (ESD) and was used as an indicator of Oscillatoria sp. Abundance, including for aggregates <45 and >100μm (ESD). In addition, air temperature, radiation and precipitation were downloaded from meteorological databases. In agreement with the meteorological annual cycle observed in air temperature, radiation and precipitation, sulfide concentration at La Hedionda Spa shows an annual cycle with concentrations around 40 μM in winter and up to 200 μM in the dry summer period. Phytoplankton composition was dominated by cyanobacteria (mainly Oscillatoria sp.), but other groups were also represented (green algae, cryptomonads, diatoms and dinoflagellates), although they remained constant throughout the year (median Chl a < 0.2 μg L−1). Cyanobacteria, in contrast, showed an annual cycle with a significantly higher median in summer (Chl a = 1.6 μg L−1) than in winter (Chl a = 0.4 μg L−1). No linear relationship between nutrients and cyanobacteria concentration was observed, but an optimum curve of cyanobacteria concentration to sulfide concentration was fitted through a general additive model (GAM). The four-fold increase of cyanobacteria concentration under exposition of an elevated sulfide concentration can be due to higher growth rates at elevated sulfide concentrations reported for an Oscillatoria sp. strain isolated during the same annual cycle at La Hedionda and we suggest that the selective agent, sulfide, positively triggers Oscillatoria sp. proliferation in summer. According to our findings, the Oscillatoria sp. population of La Hedionda not only is sulfide-resistant, but requires sulfide in its optimal niche.
... Additionally, when the concentration of the toxic element exceeds the levels of physiological adaptation, survival depends almost exclusively on adaptive evolution driven by mutations that confer resistance (Sniegowski and Lenski, 1995;Belfiore and Anderson, 2001). Genetic adaptation has allowed microalgae to thrive in extremely hostile environments under high levels of pollutants and other extreme conditions ( Costas et al., 2007Costas et al., , 2008Flores-Moya et al., 2005;Lopez-Rodas et al., 2008a,b, 2009b. Phytoplankton adaptation capacity to lindane contamination is important to understand the ecological consequences of lindane residues in aquatic ecosystems. ...
... Several classic works on adaptation of microalgae to antibiotics have found that antibiotic-resistance depends exclusively on single mutations in nuclear or chloroplast genes (Sager, 1954(Sager, , 1962(Sager, , 1977(Sager, , 1985. Similarly, recent evidence suggests that mutation at one locus can achieve adaptation of mesophile microalgae to diverse hostile natural environments ( Costas et al., 2007Costas et al., , 2008Lopez-Rodas et al., 2008a;Flores-Moya et al., 2005) as well as to severe anthropogenic contamination ( Costas et al., 2001;Lopez-Rodas et al., 2001Garcia-Villada et al., 2004). ...
... The mutation rates from lindane-sensitivity to lindaneresistance found at the two lowest concentrations (5 and 15 mg/L) were around the same ranges as those that have been described before for the resistance to several biocides in other cyanobacterial and microalgae species ( Costas et al., 2001;Lopez-Rodas et al., 2001;Baos et al., 2002;Garcia-Villada et al., 2002). However, the mutation rates at the highest concentration tested (40 mg/L: 2.35 × 10 −7 ) were one order of magnitude lower than the mutation rates that have been usually described but of the same order of magnitude than those found for the resistance to sulfureous waters in the chlorophycean Spirogyra insignis (2.7 × 10 −7 mutants per cell per generation) (Flores-Moya et al., 2005). Mutations conferring resistance to phytoplanktonic organisms inhabiting extremely toxic environments seem thereby to be rarer than those required to assure resistance at less toxic environments. ...
Lindane is especially worrisome because its persistence in aquatic ecosystems, tendency to bioaccumulation and toxicity. We studied the adaptation of freshwater cyanobacteria and microalgae to resist lindane using an experimental model to distinguish if lindane-resistant cells had their origin in random spontaneous pre-selective mutations (which occur prior to the lindane exposure), or if lindane-resistant cells arose by a mechanism of physiological acclimation during the exposure to the selective agent. Although further research is needed to determine the different mechanisms contributing to the bio-elimination of lindane, this study, however, provides an approach to the bioremediation abilities of the lindane-resistant cells. Wild type strains of the experimental organisms were exposed to increasing lindane levels to estimate lethal concentrations. Growth of wild-type cells was completely inhibited at 5mg/L concentration of lindane. However, after further incubation in lindane for several weeks, occasionally the growth of rare lindane-resistant cells was found. A fluctuation analysis demonstrated that lindane-resistant cells arise only by rare spontaneous mutations that occur randomly prior to exposure to lindane (lindane-resistance did not occur as a result of physiological mechanisms). The rate of mutation from lindane sensitivity to resistance was between 1.48 × 10(-5) and 2.35 × 10(-7) mutations per cell per generation. Lindane-resistant mutants exhibited a diminished fitness in the absence of lindane, but only these variants were able to grow at lindane concentrations higher than 5mg/L (until concentrations as high as 40 mg/L). Lindane-resistant mutants may be maintained in uncontaminated waters as the result of a balance between new resistant mutants arising from spontaneous mutation and resistant cells eliminated by natural selection waters via clone selection. The lindane-resistant cells were also used to test the potential of microalgae to remove lindane. Three concentrations (4, 15 and 40 mg/L) were chosen as a model. In these exposures the lindane-resistant cells showed a great capacity to remove lindane (until 99% lindane was eliminated). Apparently, bioremediation based on lindane-resistant cells could be a great opportunity for cleaning up of lindane- and other chlorinated organics-polluted habitats.
... However, only in 10% of field samples were sexual reproduction stages revealed, which makes identifying the species of most collected samples impossible (Berry and Lembi, 2000;Hainz et al., 2009). The sexual reproduction of Spirogyra is not easy to induce even under laboratory conditions, since the factors driving this process are almost unknown (Berry and Lembi, 2000;Flores-Moya et al., 2005). It is known that these factors may vary in different species: for example, in S. majuscule conjugation is initiated by the exhaustion of nitrogen in cells, while in other species (S. castanacea, S. fuluviatilis) the decrease in nitrogen content is not an inducer of the sexual process (Ikegaya et al., 2012). ...
... Indeed, during the identification of vegetative cells based on morphological traits, sometimes up to 15 different Spirogyra species, which in fact represent only morphs of the same species, can be detected in one sample (Berry and Lembi, 2000;Townsend et al., 2008). In addition, in the Spirogyra populations, various mutations occur quite often under the influence of external factors (Flores-Moya et al., 2005). Thus, in most studies, the species affiliation of algae of the genus Spirogyra remains unknown and the contradictions in the description of the ecological properties of algae of this genus listed below can be explained by their species differences. ...
In recent decades, alongside the comparatively well-studied bloom caused by phytoplankton, a bloom of marine and fresh waters caused by littoral benthic macroalgae of three genera-Ulva, Cladophora, and Spirogyra-have become a global phenomenon. In the present review, an attempt is made to gain an understanding of why it is these taxa of green filamentous algae that start to grow rapidly in the spring in many water bodies and streams, including oligotrophic waters, and then float up from the bottom, forming floating mats (metaphyton); then their decaying masses are washed ashore and cause substantial ecological and economical losses. Peculiar and common ecological and physiological features of Ulva, Cladophora, and Spirogyra favorable for the formation of green tides are considered. Although eutrophication (the supply of nitrogen and phosphorus from agricultural lands, industrial and domestic wastewaters, and aquaculture) is the evident cause of the increase in algal biomass, it is suggested that the location of external fluxes of inorganic nutrients (surface runoff or groundwater discharge), as well as the biogenic redirection of internal fluxes of nitrogen and phosphorus from pelagial to littoral (benthification), play a key role in the formation of green tides. Measures for controlling green tides are discussed. The necessity for detailed studies of the metaphytonic form of vegetation of benthic macroalgae is emphasized. Obviously, a revision of the present concept of oligotrophic/eutrophic waters which considers only the pelagic compartments of aquatic ecosystems is required.
... Five unexposed controls of each strain were also prepared. The growth rate (m) was calculated as previously described (Costas 1990) as follows: (Crow and Kimura 1970) where t = 7 days (exposure time to OsO 4 ) and N t and N 0 represent the cell density at the end and the beginning of the experiment, respectively. The cells in experimental treatments and controls were directly counted under an inverted microscope (Axiovert 35, Zeiss Oberkochen, Germany) using Uriglass settling chambers (Biosiga, Cona, Italy). ...
... In contrast, populations of a continental cyanobacterium and an open ocean haptophyte could not adapt to a high dose of Os. In terms of population genetics, recombination, ploidy levels, and growth rates can all affect the speed of adaptive evolution (Crow and Kimura 1970;Spiess 1989). For example, haploid organisms respond more quickly than diploids to selection because all mutations are expressed immediately. ...
To understand the vulnerability of individual species to anthropogenic contamination, it is important to evaluate the different abilities of phytoplankton to respond to environmental changes induced by pollution. The ability of a species to adapt, rather than its initial tolerance, is the basis for survival under rapidly increasing levels of anthropogenic contamination. High doses of osmium (Os) cause massive destruction of diverse phytoplankton groups. In this study, we found that the coastal chlorophyte Tetraselmis suecica and the continental chlorophyte Dictyosphaerium chlorelloides were able to adapt to a lethal dose of Os. In these species, Os-resistant cells arose as a result of rare spontaneous mutations (at rates of approximately 10(-6) mutants per cell division) that occurred before exposure to Os. The mutants remained in the microalgal populations by means of mutation-selection balance. The huge size of phytoplankton populations ensures that there are always enough Os-resistant mutants to guarantee the survival of the population under Os pollution. In contrast, we observed that neither a haptophyte species from open ocean regions nor a cyanobacterium from continental freshwater were able to adapt to the lethal Os dose. Adaptation of phytoplankton to Os contamination is relevant because industrial activities are leading to a rapid increase in Os pollution worldwide.
... In this framework, we recently proposed that algal colonization of acidic (pH 4.1–4.5), sulphureous water from La Hedionda (S Spain) spa (Flores-Moya et al., 2005) or very acid (pH 1.7–2.5) and metal-rich water from Spain's Rio Tinto (Costas et al., 2007), could be explained by natural selection of pre-selective resistant mutants of mesophilic taxa occurring in non-extreme environments. ...
... Consequently, the occurrence preselective mutations prior to exposure to MPW seems to be the sole mechanism that allows adaptation of algae to MPW. The rate of mutation from MPW-sensitivity to MPWresistance in D. chlorelloides (1.6 × 10 −6 mutants per cell division) was in the middle of the range of the mutation rates (from 2.1 × 10 −5 to 2.7 × 10 −7 mutants per cell division) we have described for resistance to several biocides and severe environments in other cyanobacteria and microalgal species (Costas et al., 2001Costas et al., , 2007 López-Rodas et al., 2001 López-Rodas et al., , 2007 Baos et al., 2002; García-Villada et al., 2002 Flores-Moya et al., 2005). Mutation from MPW-sensitivity to MPW-resistance occurs prior to exposure to MPW. ...
Microalgal adaptation to a stressful environment (acidic, metal-rich mine waters) could be due to selection of pre-selective mutants originating in non-extreme environments Abstract At least six species of eukaryotic microalgae inhabit the acidic (pH 2.4–2.7), metal-rich mine waters from ponds in the copper mine district of Mynydd Parys (N Wales, UK). Consequently, these ponds constitute interesting natural laboratories for analysis of adaptation by microalgae to extremely stressful conditions. To distinguish between the pre-selective and post-selective origin of adaptation processes that allow the existence of microalgae in these ponds, a Luria-Delbrück fluctuation analysis was performed with the chlorophycean Dictyosphaerium chlorelloides isolated from non-acidic waters. In this analysis, natural Mynydd Parys pond water (MPW) was used as selective factor. Pre-selective, resistant D. chlorelloides cells appeared with a frequency of 1.6 × 10 −6 per cell per generation. MPW-resistant mutants, with a diminished Malthusian fitness, are maintained in non-extreme waters as the result of a balance between new MPW-resistant cells arising by mutation and MPW-resistant mutants eliminated by natural selection (equilibrium at ca. 19 MPW-resistant per 10 7 wild-type cells). We propose that the microalgae inhabiting these stressful ponds could be the descendents of chance mutants that arrived in the past or are even arriving at the present.
... Studies of bacteria and protists are clearly needed, because crucially important nutrient cycles may become less predictable as essential microbes succumb to anthropogenic toxins (Woodruff 2001). In particular, since microalgae and cyanobacteria are the principal primary producers of aquatic ecosystems (Kirk 1994; Falkowski and Raven 1997), the tolerance of these organisms to contaminated environments is very relevant from an ecological point of view. Herbicides are among the most significant human-synthesized pollutants in aquatic ecosystems (Koenig 2001). ...
... Adaptation of cyanobacteria and algae, which are the principal primary producers of aquatic ecosystems, to environmental changes resulting from anthropogenic contamination (or even to extreme natural environments) seems to be the result of a rare event: the spontaneous mutation from sensitivity to resistance that occurs randomly prior to the cells coming into contact with the selective agent (Costas et al. 2001; Baos et al. 2002; García-Villada et al. 2002 FloresMoya et al. 2005). The rate of mutation from G s fi G r (from 3.1 · 10 –7 to 3.6 · 10 –7 mutants per cell per generation) was one to two orders of magnitude lower than the mutation rates we have described (from 2.12 · 10 –5 to 1.76 · 10 –6 mutants per cell per generation) for the resistance to several biocides in other cyanobacterial and microalgal species (Costas et al. 2001 ; Ló Baos et al. 2002; García-Villada et al., 2002), but of the same order of magnitude found for the resistance to sulphureous waters in the chlorophycean Spirogyra insignis (2.7 · 10 –7 mutants per cell per generation) (Flores-Moya et al. 2005 ). Nevertheless , the pre-selective G s fi G r mutations are sufficiently frequent in M. aeruginosa populations to allow them to adapt to the presence of glyphosate in culture. ...
Adaptation of Microcystis aeruginosa (Cyanobacteria) to resist the her-bicide glyphosate was analysed by using an experimental model. Growth of wild-type, glyphosate-sensitive (G s) cells was inhibited when they were cultured with 120 ppm glyphosate, but after further incubation for several weeks, occasionally the growth of rare cells resistant (G r) to the herbicide was found. A fluctuation analysis was carried out to distinguish between resistant cells arising from rare spontaneous mutations and resistant cells arising from other mechanisms of adaptation. Resistant cells arose by rare spontaneous mutations prior to the addition of glyphosate, with a rate ranging from 3.1 · 10 –7 to 3.6 · 10 –7 mutants per cell per generation in two strains of M. aeruginosa; the frequency of the G r allele ranged from 6.14 · 10 –4 to 6.54 · 10 –4 . The G r mutants are slightly elliptical in outline, whereas the G s cells are spherical. Since G r mutants have a diminished growth rate, they may be maintained in uncontaminated waters as the result of a balance between new resistants arising from spontaneous mutation and resistants eliminated by natural selection. Thus, rare spontaneous pre-selective mutations may allow the survival of M. aeruginosa in glyphosate-polluted waters via G r clone selection. Ó Springer Science+Business Media B.V. 2006
... The data of this study correspond to the results of other work carried out on understanding algal adaptation to anthropogenic chemical water pollutants Baos 2002;García-Villada 2002;Flores-Moya 2005]. The mutation rate from 3.1·10 -6 to 5.2·10 -6 mutants per cell per generation was the same order (or one order lower and higher) of magnitude found for the resistance to several pollutants in other cyanobacterial and microalgal species. ...
... This fraction of resistant mutants is presumably enough to assure the adaptation of algal populations to catastrophic water contamination, since the algal natural populations are composed of countless cells. Nevertheless, mutations usually imply an energetic cost that may affect the survival of adapting populations [Coustau 2000], as it has been demonstrated by a decreased growth rate in resistant cells compared to growth rate in sensitive ones [Flores-Moya 2005;López-Rodas 2007]. Thus, resistant cells could develop in freshwater ecosystems polluted with the toxicants, but their contribution to primary production will be significantly lower than that occurring in pristine ecosystems with sensitive cells. ...
Algae are the principal primary producers of aquatic ecosystems. Modern
chemical residues from water pollution (such as pesticides in surface
and ground waters, antibiotics, chemical substances of military use,
heavy metals, oil, oil products, etc.) are a challenge to survival of
microagal populations. Growth of many species was restricted even by
micromolar concentrations of such xenobiotics.
... However, when changes in environmental conditions exceed physiological limits, species survival will depend exclusively on adaptive evolution, which is in turn driven by the occurrence of mutations that confer resistance (Sniegowski & Lenski, 1995;Belfiore & Anderson, 2001). Previous studies on the adaptation of phytoplankton to both anthropogenic pollutants and extreme natural environments have demonstrated that physiological acclimation is optimally achieved under the least toxic conditions Carrera-Martinez et al., 2010), whereas genetic adaptation is observed in waters ostensibly lethal for the experimental organisms (Flores-Moya et al., 2005;Costas et al., 2007;López-Rodas et al., 2007, 2008a and that this adaptation is usually attained as a consequence of single mutations Costas et al., 2001). Therefore, by analyzing the growth of different phytoplankton species belonging to diverse functional groups submitted to selection pressure during many generations, the differential specific adaptation capability can be assessed. ...
... Survival and growth of phytoplankton in contaminated environments is an interesting topic from both the genetic and physiological points of view, as phytoplankton is the principal primary producer of aquatic ecosystems (Kirk, 1994;Falkowski & Raven, 1997). In fact, microalgae have been shown to be highly sensitive to the presence of this type of herbicide (Solomon et al., 1996), but herbicide sensibility varies depending on the species tested (Blank et al., 1984;Ma & Chen, 2005). ...
• Investigating the differential capacity of the response of phytoplankton to human-induced environmental forcing has become a key issue to understanding further the future repercussions on the functioning of aquatic ecosystems. • The initial tolerance to the widely dispersed herbicide simazine was measured in diverse phytoplankton species. An experimental ratchet system maintaining large populations of dividing cells (which ensures the occurrence of rare spontaneous mutations that confer adaptation) and a strong selection pressure (which ensures the preservation of such mutations within the population) was later applied to estimate the capability of different groups of phytoplankton to adapt to simazine. • Initially, simazine doses between 0.05 and 0.15 ppm were able to inhibit 100% growth in all the species tested. However, a significant increase in simazine resistance was achieved in all derived populations during the ratchet experiment. The differential capacity for simazine adaptation was observed among the different species. • The capacity of different species to adapt to simazine can be explained in relation to taxonomic group, ploidy, growth rate and habitat preference. Haploid populations of continental Chlorophyta showed the greatest capacity to adapt to simazine. By contrast, populations of Haptophyta of open ocean regions were the group least capable of adapting to the herbicide.
... The Hindon River is an accessory river of the Yamuna River in Uttar Pradesh, India (Saini et al., 2022a;Saini and Kant, 2022b). Microalgae possess a wide range of active substances in response to ecological pressure due to their biochemical and physiological characteristics (Flores- Moya et al., 2005). Algae known as desmids are referred from the families Closteriaceae, Desmidiaceae, Mesotaeniaceae and Peniaceae of the order Zygnematales. ...
In the present exploration total of 14 Cosmarium species have been reported
from nine sites of district Saharanpur (U.P.), India. Sampling was done from
the Hindon River (a tributary of the Yamuna River). In this exploration,
Cosmarium awadhense was more dominant, while Cosmarium isthmochondrum
var. isthmochondrum and Cosmarium subalatum recorded only single site. S1
24%, S2 19%, S3 16%, S4 3%, S5 not reported (0%), S6 11%, S7 6%, S8 16%, S9
5% species of Cosmarium was reported.
... In a laboratory, the top of the pipe was opened and the sedimentary part of the test column was wrapped with aluminum foil to avoid light. The Spirogyra collected from the sampling site was pre-incubated in BG-11 medium at 25°C, fluorescent light (2000 Lux), and 12:12 h light-dark cycle for 7 days, then the algae showed a well growth in terms of fresh weight (Flores-Moya et al. 2005). Twelve pipes were inoculated with Spirogyra as the algae+sediment (A+S) group and another twelve pipes contained sediment cores only as the contrast group (S group). ...
Excessive growth of filamentous green algae in rivers has attracted much attention due to their functional importance to primary production and carbon cycling. However, comprehensive knowledge of how filamentous green algae affect carbon cycling, especially the CH4 emissions from river ecosystems, remains limited. In this study, incubation experiments were conducted to examine the factors regulating CH4 emissions from a eutrophic river with dense growth of filamentous green algae Spirogyra through combinations of biogeochemical, molecular biological, and stable carbon isotope analyses. Results showed that although water dissolved oxygen (DO) in the algae+sediment (A+S) incubation groups increased up to 19 mg L−1, average CH4 flux of the groups was 13.09 μmol m−2 day−1, nearly up to two times higher than that from sediments without algae (S groups). The significant increase of sediment CH4 oxidation potential and methanotroph abundances identified the enhancing sediment CH4 oxidation during Spirogyra bloom. However, the increased water CH4 concentration was consistent with depleted water \( {\delta}^{13}{\mathrm{C}}_{{\mathrm{C}\mathrm{H}}_4} \) and decreased apparent fractionation factor (αapp), suggesting the important contribution of Spirogyra to the oxic water CH4 production. It can thus be concluded that high DO concentration during the algal bloom promoted the CH4 consumption by enhancing sediment CH4 oxidation, while algal-linked oxic water CH4 production as a major component of water CH4 promoted the CH4 emissions from the river. Our study highlights the regulation of Spirogyra in aquatic CH4 fluxes and will help to estimate accurately CH4 emissions from eutrophic rivers with dense blooms of filamentous green algae.
Graphical abstract
... Microalgae presented mutations rates of 1 resistant cell per 10 5 -10 7 sensitive cells to a wide variety of selective agents (reviewed by [73]) and huge populations. Refuting the idea that adaptation to extreme environments takes place by a gradual selection of minor effect mutations for extended periods of time [70], previous studies have addressed the role of preselective mutations in the adaptation to extreme environments in microalgae species [14,23,42,71,72]. The adaptation of microalgae to UMIWs of Spain and Portugal occurred from the early nineteenth century when mining activities started. ...
Anthropogenic extreme environments are emphasized as interesting sites for the study of evolutionary pathways, biodiversity, and extremophile bioprospection. Organisms that grow under these conditions are usually regarded as extremophiles; however, the extreme novelty of these environments may have favor adaptive radiations of facultative extremophiles. At the Iberian Peninsula, uranium mining operations have rendered highly polluted extreme environments in multiple locations. In this study, we examined the phytoplankton diversity, community structure, and possible determining factors in separate uranium mining-impacted waters. Some of these human-induced extreme environments may be able to sustain indigenous facultative extremophile phytoplankton species, as well as alleged obligate extremophiles. Therefore, we investigated the adaptation capacity of three laboratory strains, two Chlamydomonas reinhardtii and a Dictyosphaerium chlorelloides, to uranium-polluted waters. The biodiversity among the sampled waters was very low, and despite presenting unique taxonomic records, ecological patterns can be identified. The microalgae adaptation experiments indicated a gradient of ecological novelty and different phenomena of adaptation, from acclimation in some waters to non-adaptation in the harshest anthropogenic environment. Certainly, phytoplankton extremophiles might have been often overlooked, and the ability to flourish in extreme environments might be a functional feature in some neutrophilic species. Evolutionary biology and microbial biodiversity can benefit the study of recently evolved systems such as uranium-polluted waters. Moreover, anthropogenic extremophiles can be harnessed for industrial applications.
... The modification allowed carrying out the experiment with liquid cultures instead of solid medium. The running of the experiment and the interpretation of the possible results ( Fig. 1), have been extensively detailed in our previous studies (Costas et al. 2001, 2007, López-Rodas et al. 2001, 2007, 2008a,b, 2009, García-Villada et al. 2002, 2004, Flores-Moya et al. 2005, Marvá et al. 2010, Fernández-Arjona et al.2013, Melero- Jiménez et al. 2019). In short, two different sets of experimental cultures were prepared ( Fig. 1). ...
Experimental evolution studies using cyanobacteria as model organisms are scarce despite their importance in the evolution of photosynthetic organisms. For the first time three different experimental evolutionary approaches have been applied to shed light on the sulfide adaptation process, which played a key role in the evolution of this group. With this purpose, we used a Microcystis aeruginosa sulfide‐sensitive strain, unable to grow above ~0.1 mM, and an Oscillatoria sp. strain, isolated from a sulfureous spa (~0.2 mM total sulfide). Firstly, performing a fluctuation analysis design using the spa waters as selective agent, we proved that M. aeruginosa was able to adapt to this sulfide level by rare spontaneous mutations. Secondly, applying a ratchet protocol, we tested if the limit of adaptation to sulfide of the two taxa was dependent on their initial sulfide tolerance, finding that M. aeruginosa adapted to 0.4 mM sulfide, and Oscillatoria sp. to ~2 mM sulfide, twice it highest tolerance level. Thirdly, using an evolutionary rescue approach, we observed that both speed of exposure to increasing sulfide concentrations (deterioration rate) and populations' genetic variation determined the survival of M. aeruginosa at lethal sulfide levels, with a higher dependence on genetic diversity. In conclusion, sulfide adaptation of cyanobacteria sensitive strains is possible by rare spontaneous mutations and the adaptation limits depend on the sulfide level present where strains inhabit. The high genetic diversity of a sulfide‐sensitive strain, even at fast environmental deterioration rates, could increase its possibility of survival even to a severe sulfide stress. This article is protected by copyright. All rights reserved.
... The modification allowed us to carry out the experiment with liquid cultures instead of solid medium. The running of the experiment and the interpretation of the results (Fig. 1), were extensively detailed in our previous studies (Costas et al. 2001(Costas et al. , 2007López-Rodas et al. 2001, 2008a, 2008b, 2011García-Villada et al. 2002Flores-Moya et al. 2005;Marvá et al. 2010;Fernández-Arjona et al. 2013). In short, two different sets of experimental cultures were prepared. ...
The cyanobacterium Microcystis aeruginosa causes most of the harmful toxic blooms in freshwater ecosystems. Some strains of M. aeruginosa tolerate low‐medium levels of salinity, and because salinization of freshwater aquatic systems is increasing worldwide it is relevant to know what adaptive mechanisms allow tolerance to salinity. The mechanisms involved in the adaptation of M. aeruginosa to salinity (acclimation vs. genetic adaptation) were tested by a fluctuation analysis design, and then the maximum capacity of adaptation to salinity was studied by a ratchet protocol experiment. Whereas a dose of 10 g NaCl L−1 completely inhibited the growth of M. aeruginosa, salinity‐resistant genetic variants, capable of tolerating up to 14 g NaCl L−1, were isolated in the fluctuation analysis experiment. The salinity‐resistant cells arose by spontaneous mutations at a rate of 7.3 × 10−7 mutants per cell division. We observed with the ratchet protocol that three independent culture populations of M. aeruginosa were able to adapt to up to 15.1 g L−1 of NaCl, suggesting that successive mutation‐selection processes can enhance the highest salinity level to which M. aeruginosa cells can initially adapt. We propose that increasing salinity in water reservoirs could lead to the selection of salinity‐resistant mutants of M. aeruginosa.
... Microalgae had a wide range of active substances in response to the ecological pressure because of their biochemical and physiological characteristics (Flores-Moya et al. 2005) [1] . The Cosmarium sp. is a unicellular freshwater alga (Felisberto and Rodrigues 2004) [2] . ...
Cosmarium sp is unicellular microalga which was grown in bold basal medium with the controlled condition and investigated biochemical characterizations for biodiesel production and evaluated standardization of ethanol production. Once microalgae were reaches the proper growth stage total lipid was analyzed and these lipids were used for the production of biodiesel by transesterification process using Calcium oxide (0.66%) as a catalyst. Bioethanol production was done by using the defatted residues of Cosmarium sp. with Saccharomyces cerevisiae (10%). In view of the above-mentioned facts, the present study has been designed to enhance the production of biodiesel and bioethanol.
... These results are consistent with our findings. Generally, chlorophytes are successful in oil toxicity mesocosm experiments A 2 per quanta), PSII connectivity factor (q; dimensionless) and PSII re-oxidation time (lsec) measured via fast repetition rate fluorescence on 10 phytoplankton species in controls (f/2 media), water-accommodated fraction of oil (WAF), chemically enhanced WAF (CEWAF), and a diluted CEWAF (DCEWAF (Bott andRogenmuser 1978, Gilde andPinckney 2012), and have shown resilience to a variety of toxicants such as heavy metals (Baos et al. 2002, L opez-Rodas et al. 2008) and sulfur (Flores-Moya et al. 2005). However, it should be noted that not only was the baseline population of chlorophytes (prespill, 2010) in the Gulf of Mexico low (1.5%), they disappeared from the phytoplankton community entirely in 2010 following the DwH spill (Parsons et al. 2015). ...
Culture experiments were conducted on ten phytoplankton species to examine their biological and physiological responses during exposure to oil and a combination of oil and dispersant. The species tested included a range of taxa typically found in the Gulf of Mexico such as cyanobacteria, chlorophytes and diatoms. Cultures were exposed to Macondo surrogate oil using the water accommodated fraction (WAF), and dispersed oil using a chemically enhanced WAF (CEWAF) and diluted CEWAF (DCEWAF), to replicate conditions following the Deepwater Horizon spill in the Gulf of Mexico. A range of responses were observed, that could broadly class the algae as either “robust” or “sensitive” to oil and/or dispersant exposure. Robust algae were identified as Synechococcus elongatus, Dunaliella tertiolecta, two pennate diatoms Phaeodactylum tricornutum and Navicula sp., and Skeletonema grethae CCMP775, and were largely unaffected by any of the treatments (no changes to growth rate or time spent in lag phase relative to controls). The rest of the phytoplankton, all centric diatoms, exhibited at least some combination of reduced growth rates or increased lag time in response to oil and/or dispersant exposure. Photophysiology did not have a strong treatment effect, with significant inhibition of photosynthetic efficiency (Fv/Fm) only observed in the CEWAF, if at all. We find that the effects of oil and dispersants on phytoplankton physiology are species-dependent, and not always detrimental. This has significant implications on how oil spills might impact phytoplankton community structure and bloom dynamics in the Gulf of Mexico, which in turn impacts higher trophic levels.
... > Synechococcus sp, while among Mariut lake members the order of lindane tolerance was Microcystis aeruginosa MA1 > Anabaena cylindrica > M. aeruginosa MA15 > A. spiroides > A. flosaquae. Evidences suggest that mutation at one locus in the chromosome of bacteria can change and make adaptation to the diverse hostile contaminated sites (Flores-Moya et al. 2005;Costas et al. 2007Costas et al. , 2008Lopez-Rodas et al. 2008a) as well pathogenic potentials Lopez-Rodas et al. 2001Garcia-Villada et al. 2004). Lindane-resistant cells of microalgae Scenedesmus intermedius (Clorophyta) were able to eliminate lindane (5-40 mg/L) efficiently (González et al. 2012). ...
Hexachlorocyclohexane (HCH), commonly known as lindane, is the term which collectively identifies the eight isomers of the HCH. The lindane has only insecticidal properties and also considered as most toxic isomer of the HCH. The lindane has been listed as a persistent organic pollutant (POPs) under Stockholm Convention on June 29, 2005. More than 52 countries not only globally banned for its formulation but also use of lindane in any form. After knowing facts regarding its toxicity, persistence nature, and bioaccumulation, some countries are still producing and exporting the lindane on large scale. The countries involved in lindane formulation are creating dumping sites which are the major source of lindane contamination to the adjoining area. The lindane deposited in the cultivated soils where they are applied are also affecting to the non-target organisms. Apart from this, scientists start working on its degradation and find out that bioremediation is the easiest, cheapest,
and safest way to remove the lindane from contaminated sites. Bioremediation by the microalgae could help in decontaminating polluted aquatic ecosystems and in cleaning the effluents before they are discharged into aquatic systems. Many microorganisms show tremendous potential in lindane degradation. The present review article describes about all known possible lindane-degrading microorganisms used for its bioremediation and also concise advanced techniques used for this purpose.
... Resistant mutants of microalgae are usually used to manufacture specific biosensors (44,45). This capability is perhaps a consequence of microalgae ability for adaptation to hostile natural environments by mechanisms based on single mutations (46)(47)(48)(49)(50). ...
... Toxicants killed susceptible cells of wild type but allowed the growth of resistant cells. Luria-Delbruck fluctuation test has shown that in S. quadricauda and T. weissflogii the rate of mutation was respectively 5.2 × 10 -6 and 3.1 × 10 -6 mutants (calculated per division) resistant to chrome and 4.1 × 10 ⎯7 mutants of S. quadricauda resistant to strep tomycin and was comparable to the rates of spontane ous mutations estimated by different researchers upon the investigation of resistance of other algal species to some toxicants but turned out to be two orders of mag nitude higher than in bacteria [22,23]. The recurrent occurrence of rare spontaneous preselective mutations ensures the survival of such populations upon the pollu tion of the environment. ...
Effect of colloidal silver nanoparticles on growth and structure of laboratory populations was investigated in chlorococcal algae Scenedesmus quadricauda (Turp.) Bréb. and Monoraphidium arcuatum (Korsch.) Hind. in the range of concentrations from 0.0001 to 1 mg/L. The toxicity of colloidal silver was manifested at a concentration of 0.1 mg/L and higher and was associated with an algostatic effect, which duration directly depended on silver concentration in the medium. After a period of growth suppression at a concentration of 0.1 mg/L, in both species cell population in the culture was gradually recovered and the structure of population (ratio between the fractions of dividing, quiescent, and dead cells) became the same as in control material. The effect of adaptation of S. quadricauda to colloidal silver was detected upon successive passages to the media with toxic concentrations (0.1 and 0.5 mg/L), which depended on the concentration and duration of initial intoxication of the culture. The toxicity of cell-free filtrates from the culture of S. quadricauda, which was in contact with colloidal silver for different time periods, was estimated using intact culture of the same species, whose population on cell-free filtrates was close to control level. Transfer of the cells that were exposed to silver to a pure medium led to a long lag phase in all the cases. It is assumed that the main mechanism of algal population adaptation to higher concentrations (0.1 and 0.5 mg/L) of this toxicant depends on the selection of resistant cells present in the initial heterogeneous population in the course of primary exposure to colloidal silver. These resistant cells accidentally emerge in the population by means of rare spontaneous mutations occurring in the course of replication even before the contact with silver and have more perfect mechanisms of its detoxification.
... This pattern was observed by first time in the Guadiamar River (S, Spain) after the toxic heavy metal spill of Aznalcollar mine (35) and confirmed in the heavy metal contaminated environments of Aguas Agrias, Spain (36), Mynydd Parys, Wales, UK (37), and Rio Tinto, Spain (38). In la Hedionda, Spain, an example of extreme sulphureus waters, also proliferate a few mesophile Chlorophyta species (39). ...
Nowadays, accidental spills of crude oil are one of the most worrisome environmental problems. Usually, the crude oil spills rapidly inhibited photosynthesis of microalgae (the main primary producers of aquatic ecosystems) causing a severe damage to inland waters ad marine ecosystems. In order to add knowledge about microalgal response to crude oil spill, here we study a fascinating example of extreme contamination by crude oil spills continuously (at least since 1915) in Arroyo Minero, Nirihuan de Arriba, Río Negro, Argentina. This study is changing our pre-conceived ideas on the adaptation of microalgae to crude oil. Astonishingly, a high biomass of microalgae proliferates in contact with crude oil. In contrast with the paradox of the plankton (which predict that more than 30 microalgal species would coexist in the same water body) only four species were detected in the crude oil spill area. They are cosmopolitan mesophile species and not extremophile ones (as would be expected). The most abundant species was the Chlorophyta Scenedesmus obtusus. Other abundant species seems to be a new Scenedesmus species. The other two species Symploca dubia Cyanobacteria and Chlamydomonas dinobryonis Chlorophyta are new records for flora of Argentina. These species were isolated maintained in clonal laboratory cultures and characterised. They are resistant to crude oil of Arroyo Minero and to analytical petroleum special standard. In contrast similar species isolated from areas without crude oil contamination were destroyed by petroleum.
... In this work, we carried out a mechanistic approach to disentangling causes of adaptation of phytoplankton to temperature increase. Based on classic concepts on adaptation to environmental change (Fisher, 1930;Lewontin, 1974;Sniegowski & Lensky, 1995), and recent experimental work on adaptation of phytoplankton to global change (Garcia-Villada et al., 2004;López-Rodas, Maneiro, Lanzarot, Perdigones, & Costas, 2008;Marvá, García-Balboa, Baselga-Cervera, & Costas, 2014;García-Balboa et al., 2013), and warming (Flores-Moya et al., 2005;Huertas et al., 2011;Rouco, López-Rodas, Flores-Moya, & Costas, 2011;Romero, López-Rodas, & Costas, 2012), we hypothesise a conceptual model to explain phytoplankton adaptation to temperature increase: i) under low levels of environmental stress, physiological acclimatization would be able to allow adaptation; ...
Global warming represents a challenge to the survival of phytoplankton organisms, which are the basis of the
aquatic food web and drive essential biogeochemical cycles. We propose a direct experimental research
mimicking temperature-increasing scenarios as a novel way to explore the adaptation of phytoplankton to
predicted future thermal scenarios. This vulnerability analysis of individual phytoplankton species to increased
temperature is key to understand the impact of global warming on aquatic ecosystems. Considering the
polyphyletic complexity of the phytoplankton community, we compare the adaptation ability of diverse
phytoplankton species from oceanic, coastal and inland waters to global warming, evaluating the role played by
physiological acclimatization and genetic adaptation. We found that physiological acclimatization allows survival
under the lowest temperature increase. Afterwards pre-existing genetic variability allow some genotypes to
survive. Finally, when the temperature rises to a certain threshold, only the occurrence of new mutations that
confer thermal resistance assures adaptation. Our results also reveal diverse degrees of tolerance to temperature
increase among the different functional groups of phytoplankton, with great inter-specific capacity for genetic
adaptation
... Microalgae are able to survive short-term unpredictable environmental stress by means of physiological acclimatisation by modifying gene expression (Bradshaw and Hardwick, 1989;Fogg, 2001;Costas et al., 2008). However, when the environmental stress exceeds physiological limits, only mutations that confer resistance can allow adaptation (Sniegowski and Lenski, 1995;Lopez-Rodas et al., 2001;Costas et al., 2001;Flores-Moya et al., 2005;Sniegowski, 2005). ...
... Accurate mutation rate calculations often come from repeated culture of simple organisms (e.g. algae) in the laboratory (Flores-Moya et al., 2005), or from composite data sets regarding human disease (e.g. colorectal cancer) or disorders (Giannelli et al., 1999;Repping et al., 2003). ...
Empirical work assessing the maintenance of rare genotypes in natural populations is difficult over very long time scales. Skirting this problematic issue is possible with theory and simulations. Major theoretical constructs, including mutation-selection balance and balancing selection, explain the theoretical maintenance of rare genotypes, and the occurrence of multiple, rare genotypes over time. Additionally, numerical simulations are valuable tools for assessing evolving biological systems because they allow for monitoring systems over long time scales, as well as for controlling model parameters, thus contributing to the exploration of system dynamics that cannot be assessed in nature. Here we employed numerical simulations to explore the importance of several biological factors that contribute to the maintenance of a fish color-pattern polymorphism. We present a numerical model of a two-morph fish polymorphism that allowed us to test the sensitivity of the rare morph's persistence and the population's stability to multiple parameters. Our simulations ran over 10,000 years (where one year is approximately one generation) and demonstrated the maintenance of a stable polymorphism with a rare morph which persisted at a frequency of ∼10−2, which is in-fact the frequency of the rare, mottled black mosquitofish morph in natural populations. This pigmentation polymorphism is stable, independent of changes in population size, but can be destabilized with very high predation when coupled with very low birth rates. Employing models with empirical fitness estimates is a valuable tool for monitoring rare vertebrate morphs in nature, however few studies exist that have accomplished this task. Our approach can be adapted for modeling rare morphs (particularly in additional live-bearing fishes like sailfin mollies) that also harbor rare, pigmentation morphs within large populations.
... Accurate mutation rate calculations often come from repeated culture of simple organisms (e.g. algae) in the laboratory (Flores-Moya et al., 2005), or from composite data sets regarding human disease (e.g. colorectal cancer) or disorders (Giannelli et al., 1999;Repping et al., 2003). ...
Empirical work assessing the maintenance of rare genotypes in natural populations is difficult over very long time scales. Skirting this problematic issue is possible with theory. Major theoretical constructs, including mutation-selection balance and balancing selection, explain the maintenance of very rare genotypes and the occurrence of multiple, rare genotypes over time. Numerical simulations are similarly valuable tools for assessing evolving biological systems because they allow for their monitoring over long time scales, as well as for controlling model parameters thus allowing for the exploration of dynamics that cannot be assessed in nature. Here we employed numerical simulations to explore the importance of several biological factors that contribute to the maintenance of a color-pattern polymorphism in fish. We present a numerical model of a two-morph polymorphism that allowed us to test the sensitivity of the rare morph's persistence and the population's stability to multiple parameters. Our simulations ran over 10,000 years and demonstrated the maintenance of a stable polymorphism with a rare morph that persists at a frequency of ∼10(-2), which is in-fact the frequency of the melanic pigmented mosquitofish in natural populations with melanism. This polymorphism is stable, independent of changes in population size, but can be destabilized with very high predation when coupled with very low birth rates. Employing models with empirical fitness estimates is a valuable tool for monitoring rare vertebrate morphs in nature; however, few studies exist that have accomplished this task. Our approach can be adapted for modeling rare morphs in additional live-bearing fishes (e.g. sailfin mollies) that also harbor rare melanic morphs within large populations.
... Selection of resistant mutants occurring spontaneously in nonextreme environments that repeatedly arrived at the river has been recently proposed as a mechanism to explain the rapid colonization of the Spanish Rio Tinto by algae (Costas et al. 2007 ). Similarly, Moya et al. (2005) suggested that algae inhabiting the acidic, sulfureous water of La Hedionda spa (S Spain) could have originated by selection of mutants of algal lineages from nonextreme environments (see comment in Sniegowski 2005). Another curious example is the genetic adaptation of D. chlorelloides by a single mutation to the acidic waters from a pond on Vulcano Island (S Italy) (López-Rodas et al. 2009). ...
We tested if different adaptation strategies were linked to a stress gradient in phytoplankton cells. For this purpose, we studied the adaptation and acclimation of Dictyosphaerium chlorelloides (Naumann) Komarek et Perman (Chlorophyta) and Microcystis aeruginosa (Kutz.) Kutz. (Cyanobacteria) to different water samples (from extremely acid, metal-rich water to moderate stressful conditions) of the Agrio River-Caviahue Lake system (Neuquen, Argentina). Both experimental strains were isolated from pristine, slightly alkaline waters. To distinguish between physiological acclimation and genetic adaptation (an adaptive evolution event), a modified Luria-Delbruck fluctuation analysis was carried out with both species by using as selective agent sample waters from different points along the stress gradient. M. aeruginosa did not acclimate to any of the waters tested from different points along the stress gradient nor did D. chlorelloides to the two most acidic and metal-rich waters. However, D. chlorelloides proliferated by rapid genetic adaptation, as the consequence of a single mutation (5.4 x 10)(7) resistant mutants per cell per division) at one locus, in less extreme water and also by acclimation in the least extreme water. It is hypothesized that the stress gradient resulted in different strategies of adaptation in phytoplankton cells from nonextreme waters. Thus, very extreme conditions were lethal for both organisms, but as stressful conditions decreased, adaptation of D. chlorelloides cells was possible by the selection of resistant mutants, and in less extreme conditions, by acclimation.
... Although fluctuation analysis has been proved to be the most sensitive approach to distinguish between rare spontaneous mutation and direct adaptation to environmental selection (Cole et al. 1976), the study of mutation rates in groups other than bacteria has been hampered by certain cumbersome aspects of the analysis (Rossman et al. 1995). This study is a complement to other work carried out in a framework focused on understanding phytoplankton adaptation to extreme natural conditions (Flores Moya et al. 2005; Costas et al. 2007; López-Rodas et al. 2008a,b). In this way, here we show that survival and proliferation of phytoplankters in an extreme natural pond on Vulcano Island could be achieved as a result of rare spontaneous mutations at one or a small number of loci. ...
Four species of eukaryotic algae proliferate in the sulfureous, acidic (pH 3.1) water of the largest geothermal pond on Vulcano Island (southern Italy). Consequently, this pond constitutes a natural laboratory for analysis of adaptation by phytoplankters to extremely stressful conditions. To distinguish between the pre-selective or post-selective origin of adaptation processes allowing the existence of phytoplankters in the pond, a Luria-Delbrück fluctuation test was carried out with the chlorophycean Dictyosphaerium chlorelloides and the cyanobacterium Microcystis aeruginosa, both isolated from non-extreme waters; natural water from the Vulcano Island pond was used as selective factor. Preselective, resistant D. chlorelloides cells appeared with a frequency of 4.7 × 10−7 per cell per generation. We propose that the micro-algae inhabiting this stressful pond could be the descendents of chance mutants that arrived in the past or are even arriving at the present. The genetic adaptation of D. chlorelloides to Vulcano waters could help to explain the survival of photosynthesizers in very stressful geothermal waters during the Neoproterozoic ‘snowball Earth’, a period when primary production collapsed in the biosphere. On the other hand, adaptation to these conditions was not observed in M. aeruginosa, suggesting that cyanobacteria may not be able to develop any kind of adaptation to Vulcano pond water.
... Even for organisms, where sexual reproduction is not known, the rate of asexual recombination could be higher than is commonly supposed (Drake et al., 1998). Spontaneous mutations in microalgae, for which sexual reproduction is not known (the majority of strains in the present study) or for cultures containing a single mating type (e.g., Chlamydomonas reinhardtii or Chlorogonium elongatum), may still be sufficiently frequent to form subpopulations that are adapted to extreme environments (Drake et al., 1998;Flores-Moya et al., 2005). The findings reported in the present study can be interpreted such that cryopreservation (particularly where a suboptimal protocol is applied) may lead to the selection of subpopulations, which differ in their genotypic properties as compared to their nonfrozen counterparts, but in the absence of phenotypic changes, may not represent a selective advantage. ...
Cryopreservation is the long-term, indefinite storage of living biological resources at ultralow temperatures. It is almost universally assumed that cryogenic storage supports genetic and phenotypic stability of organisms. However, certain components of the cryopreservation process, particularly some cryoprotective additives (CPAs) and free radical mediated cryoinjury, may potentially cause genetic alterations. Genetic integrity in cryopreserved microalgae was assessed using a very sensitive molecular fingerprinting technique, AFLP, on 28 terrestrial microalgal strains. In about half of all investigated strains the AFLP fingerprints revealed, with high levels of reproducibility, clearly detectable genomic differences after cryopreservation employing a widely used standard two-step cooling protocol. Differences ranged from a single fragment position to multiple fragment changes and were compared to differences found between wild-type and UV-light- or radioisotope-induced mutants of Parachlorella kessleri. The basis of the changes are discussed in terms of their reversibility, as may be the case if they are attributed to DNA methylation and/or whether they are true mutations that may potentially manifest in the phenotype. The possibility that cryopreservation selects for genotypically different subpopulations of microalgae is also considered.
... 15 Furthermore, several investigations have demonstrated that the adaptation of some eukaryotic microorganisms to extreme environments, including the AAS, may be due to preadaptive mutations and the subsequent selection of resistant mutants. 8,9,26 However, the role of preadaptive mutation in fungal adaptation to extreme environments has not yet been explored. ...
There is an increasing interest in the study of microorganisms that inhabit extreme environments for reasons that vary from gaining insight into the origin of life to the searching of new biotechnological applications.
In this work, we studied the tolerance of fungi isolated from the Aguas Agrias Stream (AAS; Tharsis, Huelva, Spain), an acidic metal-rich environment, to a culture medium prepared with water from this extreme ecosystem (AASW medium). The ability of some culture collection strains of moulds and yeasts to grow on AASW medium was also assessed.
For moulds, a tolerance index was calculated by dividing the growth diameter of colonies on AASW medium by the diameter in the control medium, and their germinative potential was recorded. For yeasts and yeast-like fungi, the minimum inhibitory concentration of AASW was determined.
In general, the fungi isolated from the AAS showed differences in their ability to germinate and grow on AASW medium. Collection strains of the genus Aspergillus could grow on AASW medium, but showed some differences in tolerance when compared to environmental isolates.
Extremotolerant fungi can manifest differences in their tolerance to culture media that simulate the conditions of their natural habitat. The results of this work suggest that the ability of fungi to grow in acidic, metal-rich environments might be more widespread than previously thought, and highlight the importance of determining the factors that are responsible for tolerance to these extreme environments.
... This superior adaptation of LLAI was possibly due to its original habitat being a natural medium as opposed to the standardized growth medium of type strains. As it has been found in the past studies that algal strains isolated from natural habitats generally have flexibility in their systems that allows them to undergo physiological adaptation or genetic mutation strains in stressed environments [72]. This flexibility in the system of isolated algae strains enables them to adapt to a new growth environment better than pure strains, which probably have much hardened system resistive to any physiological or genetic changes [73]. ...
Nutrients present in digested animal waste can be utilized for algae cultivation under suitable conditions. Algal growth, however, depends on the chemical forms and speciation of these nutrients. In this study a chemical equilibrium model was first used to describe nutrient speciation and predict conditions that enhance the solubility of nutrients in anaerobic digester effluent. Dilution with water and separation of large particulates greatly improved nutrient availability and light penetration - conditions favorable for algal cultivation. Algae growth was tested using three strains - Scenedesmus dimorphous (UTEX # 417), Chlorella vulgaris (UTEX# 265), and an algal isolate (designated as LLAI and later identified to be closely related to Chlorella vulgaris) from the wastewater treatment lagoons in Logan, UT. All tested strains could be adapted to the effluent to enhance the utilization of native nutrients present in both organic and inorganic forms. There was a marked improvement in growth rates (up to 4.8-fold) and biomass production (up to 8.7-fold) of algal cultures after they adapted to the effluent. Also, effluent-adapted strains were able to switch from phototrophy to heterotrophy to prolong the growth when light availability became limited. However, an increase in irradiance levels in light-limited cultures led to resumption of phototrophic growth. It was found that this approach of light supplementation prolonged growth and increased biomass production (up to 2.7-fold) in algal cultures. Of all the strains tested, the isolate from the wastewater treating lagoons grew to highest culture densities and produced the highest concentration of intracellular triacylglycerides (TAG). This culture also grew best in non-sterile, native effluent and could reach biomass concentration of up to 4.5g/L with TAG content of approximately 10% (w/w). Culture densities were lower when this organism was grown in sterilized effluent or in sterile artificial media, suggesting that this organism symbiotically associated with other microbes in digested animal waste. Findings of this research study suggest that microalgae can be grown efficiently on inexpensive natural substrates in non-sterile growth conditions. When commercially implemented, biodiesel production from such systems could be more cost effective and sustainable.
... The high fluctuation in the number of herbicide-resistant cells observed in set 1 cultures, in contrast with low fluctuation of set 2 controls, shows that herbicide-resistant cells have arisen from rare, pre-selective spontaneous mutations occurring randomly during replication of organisms prior to exposure to the herbicides. The mutation rates from simazine-sensitivity to simazineresistance in the three stains of microalgae (3.0–9.2 × 10 −6 mutants per cell per generation) were found to be in the middle of the range of the mutations rates (from 2.1 × 10 −5 to 2.7 × 10 −7 mutants per cell per generation) we have described in cyanobacteria and microalgae, for resistance to many other biocides and extreme natural environments (Costas et al., 2001; López-Rodas et al., 2001; Baos et al., 2002; García-Villada et al., 2002, 2004 Flores-Moya et al., 2005; Costas et al., 2007 Costas et al., , 2008 López-Rodas et al., 2007 López-Rodas et al., , 2008a López-Rodas et al., ,b,c, 2009 ). However, diquat-resistant cells appear spontaneously in wild populations with a frequency one order magnitude higher (17.9 × 10 −6 ) than simazine-resistant cells. ...
Aquatic ecosystems located close to agricultural areas are increasingly polluted by herbicides. We evaluated the capacity for adaptation of green microalgae to lethal concentrations of the herbicide simazine in one strain of Dictyosphaerium chlorelloides and two strains of Scenedesmus intermedius, as well as adaptation to the herbicide diquat in one of the strains of S. intermedius. A Luria-Delbrück fluctuation analysis was carried out in order to distinguish between resistant cells arising from physiological adaptation (acclimatization) or post-adaptive mutation (both events occurring after the exposure to the herbicides), and adaptation due to mutations before the exposure to the herbicides. Simazine-resistant cells arose by rare spontaneous mutations before the exposure to simazine, with a rate of 3.0 x 10(-6) mutants per cell per generation in both strains of S. intermedius, and of 9.2 x 10(-6) mutants per cell per generation in D. chlorelloides. Diquat-resistant cells in S. intermedius arose by pre-selective mutations with a rate of 17.9 x 10(-6) per cell per generation. Rare, pre-selective mutations may allow the survival of green microalgae in simazine- or diquat-polluted waters, via herbicide-resistant selection. Therefore, human-synthesized pollutants, such as the herbicides simazine and diquat, could cause the emergence of evolutionary novelties in aquatic environments.
An immense scientific effort has been made worldwide due to Covid-19s pandemic magnitude. It has made possible to identify almost 300,000 SARS-CoV-2 different genetic variants, connecting them with clinical and epidemiological findings. Among this immense data collection, that constitutes the biggest evolutionary experiment in history, is buried the answer to what will happen in the future. Will new strains, more contagious than the current ones or resistant to the vaccines, arise by mutation? Although theoretic population genetics is, by far, the most powerful tool we have to do an accurate prediction, it has been barely used for the study of SARS-CoV-2 due to its conceptual difficulty. Having in mind that the size of the SARS-CoV-2 population is astronomical we can apply a discrete treatment, based on the branching process method, Fokker-Plank equations and Kolmogoroffs forward equations, to calculate the survival likelihood through time, to elucidate the likelihood to become dominant genotypes and how long will this take, for new SARS-CoV-2 mutants depending on their selective advantage. Results show that most of the new mutants that will arise in the SARS-CoV-2 meta-population will stay at very low frequencies. However, some few new mutants, significantly more infectious than current ones, will still emerge and become dominant in the population favoured by a great selective advantage. Far from showing a mutational meltdown, SARS-CoV-2 meta-population will increase its fitness becoming more infective. There is a probability, small but finite, that new mutants arise resistant to some vaccines. High infected numbers and slow vaccination programs will significantly increase this likelihood.
Microalgae are ideal phototrophs for many commercial products. Our previous research has leveraged biodiversity concepts to evaluate the effects of competition on dynamics and coexistence of different microalgal species. The originality of the review lies in the envisioning of these state‐of‐the‐art techniques to study a novel issue of how algal species modulate the whole‐cell metabolism and gene expression to yield biomass beyond current limits. Competition is crucial in driving the activity, structure and composition of algal communities which are of central importance to aquatic environment productivity. However, fundamental gaps remain in understanding how algal species compete for light and nitrogen by regulating whole‐cell metabolisms. Moreover, it is unclear how this competitive potential is modulated in algal populations to achieve high biomass production. Despite the principles and applications of competition having been tested theoretically and empirically in many studies, there is still considerable debate and paradoxical observations regarding the key mechanisms that underlie competition for limited nutrients. One reason for the uncertainty is the difficulty in making direct comparisons between species with differing functional traits. Moreover, the lack of available reference genomes for many algal species presents a further hindrance in understanding competitive trait dynamics. The review seeks to improve our understanding of these fundamental problems, which have direct implications in aiding the production of renewable fuels and chemicals via photosynthetic biology. The review also envisions a whole set of omics analysis in the future that would shed light on the poorly defined functions of competition in microalgae.
A thermotolerant Desmid was isolated from Tunisian geothermal spring (Ain-Echfa) in the region of Korbous northeast of Tunisia. Under light microscope, this alga was identified as belonging to the genus Cosmarium. Combined effect of light intensity and temperature on biochemical composition (carbohydrate, lipid and protein) of this strain was evaluated using a 32 factorial design. This design was carried out with light levels of 20, 70, and 120 µmol photons m-2 s-1 and temperature of 15, 30 and 45 °C. Our findings revealed that, at the stationary stage, the major compound of Cosmarium sp was the carbohydrate with a maximum of 81.8%. Statistical analysis demonstrated that biochemical composition of this strain was mainly influenced by light intensity. The experimental design showed that, the highest levels of protein, carbohydrate and lipid were obtained at the lowest light intensity (20 μmol photons m−2 s−1). Keywords: Cosmarium; light; temperature; biochemical composition; modeling.
The term 'experimental evolution' refers to short-term evolutionary experiments with microorganisms under controlled conditions in which selection is expected to occur. In combination with whole-genome sequencing and genetic engineering, the method has become a powerful tool to study evolutionary mechanisms and engineer new microbial variants. It has been most extensively used in the model species Escherichia coli and Saccharomyces cerevisiae, but more recently photosynthetic microorganisms have been subjected to experimental evolution. In such assays, strains were generated that had become more tolerant to certain abiotic environmental factors or evolved new traits during co-propagation with other organisms. These strains were viable under conditions that were lethal to the non-adapted progenitor and in a few cases, the causative mutations were identified. Because cyanobacteria like Synechocystis or green algae like Chlamydomonas reinhardtii share many features with crop plants - which are not amenable to such experiments - experimental evolution with photosynthetic microorganisms has the potential to identify novel targets for improving the capacity of plants to acclimate to environmental change. Here, I provide a survey of the experiments performed so far in cyanobacteria and green algae, focusing on Synechocystis and C. reinhardtii, and discuss the promise and the challenges of such approaches.
In the current scenario of global change, the impact of anthropogenic stressors is affecting the aquatic ecosystems, especially essential microorganisms such as phytoplankton, driving toward a biodiversity crisis. Classic ecotoxicology studies, focused on the immediate tolerance to pollution, have provide an over simplistic understanding of the long time impact of pollutants on phytoplankton (because of the usual misconception that evolutionary changes can only take place at long-term), inadequate to enable a suitable environmental risk assessment (ERA). Currently, concepts such as predictive ecology and integrating strategies are rising rapidly in prominence with regard to forecasting phytoplankton response to human impact. This review compiles the state of the art of multigenerational and evolutionary experimental studies and the mechanisms that trigger rapid adaptation in phytoplankton to anthropogenic stressors, highlighting the importance of ecology and evolution. Ecological realisms is one of the challenging parts of the stressors hazard, considering the broad phytoplankton diversity and the multifactorial character of the natural ambiances. Field and community experiments contribute to a better discerning of ecology interactions and network relations. Moreover, laboratory experiments exploring evolutionary mechanisms that allow rapid adaptation to contaminants (e.g., fluctuation analysis or ratchet procedures) have proven to be useful linking concentration of pollutants and adaptation strategy. When environmental change exceeds the range of variation that can be coped with by organisms through plasticity, selection processes may occur and evolutionary dynamics take place. Ecology and evolution are necessary to enhance the ERA knowledge and novel experiments may well emerge from the when contemplated as whole.
Laboratory populations of microalgae are widely used as sensitive test objects for the phytotoxicity of chemicals and wastewater streams evaluation. The laboratory cultures of freshwater green alga Scenedesmus quadricauda (Turp.) Breb. and marine diatom alga Thalassiosira weissflogii (Grunow) Fryxell et Hastle were studied under pollution impact. As toxicants we used heavy metals (chromium and silver as a part of waterdissolved salt, experiments both with freshwater and marine algae) and pesticide (imazalil sulfate, experiments only with freshwater algae). The simultaneous presence of two groups of S. quadricauda cells ("large", 4.0-4.5 m in width, mainly in the composition of two-cellular coenobia, and "small", 3.0 m in width in the composition of four-cellular coenobia) proved to be a specific feature of the dimensional-age structure of the control population at different stages of its growth. This structure allows analyzing any possible changes in cell population both in normal and toxicant pressure conditions and to predict which cell cycle stage is disturbed. The dimensional-age structure analysis for diatom alga culture is complicated significantly because of their propagation features. At low metal concentrations (0.0001, 0.001 and 0.01 mg/L) and low pesticide concentration (0.001 mg/L) the total cell number decreased as compare to the control one. The reason of possible population growth delay under low-level toxic exposure was the arrest of proliferation of some cells (probably, the most sensitive cells within heterogeneous population) rather than cell cycle slowdown in all cells. Notice, that the differences between control and sample cultures at low concentrations were reversible during the period of experiment. At medium toxicant concentrations (0.05 mg/L silver, 0.1 mg/L chromium and 0.1 mg/L imazalil) the effect varied from indifferent to toxic according to algal species and season. At concentration of 0.1 mg/L chromium and imazalil the division of cells resumed within 1-2 days of intoxication. At concentrations of the toxicants over 0.05 mg/L for silver and over 1.0 mg/L for chromium and imazalil a total cell number and proportion of living cells decreased. Imazalil sulfate at concentration 1.0 mg/L was found to inhibit the division of cells and imparted to them anomalous increase in size and the formation of gigantic cells. Such state of algae was reversible: giant cells rapidly resumed their division after being transferred to a toxicantfree medium. At the concentration 3.0 mg/L chromium we observed both undividing and proliferating cells. At high toxicant concentrations (0.1 and 0.5 mg/L silver; 10.0 mg/L chromium; 5.0, 10.0 and 20.0 mg/L imazalil) cell division stimulation preceded the fast death of algal population and the small immature cells predominated in the beginning of the treatment. Only the high-level toxicant treatment caused photosynthetic efficiency reducing twice as compared to the control level. On the whole, the freshwater algae were found to be more sensitive to heavy metal action than marine algae. It was shown the existence of algostatic effect of silver after the growth of algal cultures in the presence of high toxicant concentrations. In this case the cell number stayed particularly unchangeable during the period of the experiment. S. quadricauda adaptation to extreme environmental pressure was analyzed by using an experimental model of the multiple intoxication (triple 10.0 mg/L chromium intoxication and double 1.0 mg/L silver intoxication). The selection of the resistant algal cells in the presence of high toxicant concentrations was demonstrated. These cells could restore the algal population. It is concluded that there are initial resistant cell number within the heterogenous algal population is 3-7 % (depending on toxicant) of initial cell number. A modified fluctuation analysis was performed to distinguish resistant cells within S. quadricauda and T. weissflogii laboratory cultures that had originated as a result of random spontaneous pre-selective mutations (prior to chromium exposure) from those arising through acquired post-selective adaptation (during the exposure to chromium). The changes of population structure of freshwater green alga S. quadricauda and marine diatom alga T. weissflogii were studied under different regimens of chromium exposure. Data on the cell number, their photosynthetic characteristics, population structure and share of alive and dead cells will be appropriate for use to predict the most sensitive ecosystem responses and indicate the permissible amount of toxicants in the environment. These data may have important implications for design and interpretations of the bioassay, especially within the context of the hazard/risk assessment.
Nowadays, we are living in a rapid global change period in which around 30,000 species go extinct annually due to those human activities that are altering biosphere-level biogeochemistry processes. Biosphere level cycles may become less predictable as essential microbes succumb to climatic change and anthropogenic activities. In particular, since microalgae and cyanobacteria play an important role in control of global change because they are the principal primary producers of aquatic ecosystems producing around 50% total photosynthesis. Balance between respiration -oxidation (C6H 12O6 + 6 O2 ⇒ 6 CO2 + 6 H 2O) and photosynthesis (6 CO2 + 6 H2O ⇒ C6H12O6 + 6 O2) is the pacemaker of CO2 and consequently of climatic change. Investigating the differential capacity of the response of phytoplankton to human-induced environmental forcing has become a key issue to understanding further the future repercussions on the functioning of ecosystems at planetary level. Our studies show that different functional phytoplanktonic groups (ie. oceanic, coastal, coral-simbionts, continental phytoplankton...) have very different capability for adaptation to global change. The capacity of different microalgal species to adapt to global change can be explained in relation to population genetics structure, growth rate, mutation rate, ploidy, habitat preference and taxonomic group. Populations of oceanic microalgae showed the minimal capacity to adapt to change. Since open ocean is the biggest ecosystem on the Earth, future perspectives are not good.
Laboratory populations of microalgae are widely used as sensitive test objects for the phytotoxicity of chemicals and wastewater streams evaluation. The laboratory cultures of freshwater green alga Scenedesmus quadricauda (Turp.) Breb. and marine diatom alga Thalassiosira weissflogii (Grunow) Fryxell et Hastle were studied under pollution impact. As toxicants we used heavy metals (chromium and silver as a part of water-dissolved salt, experiments both with freshwater and marine algae) and pesticide (imazalil sulfate, experiments only with freshwater algae). The simultaneous presence of two groups of S. quadricauda cells ("large", 4.0-4.5 μm in width, mainly in the composition of two-cellular coenobia, and "small", 3.0 μm in width in the composition of four-cellular coenobia) proved to be a specific feature of the dimensional-age structure of the control population at different stages of its growth. This structure allows analyzing any possible changes in cell population both in normal and toxicant pressure conditions and to predict which cell cycle stage is disturbed. The dimensional-age structure analysis for diatom alga culture is complicated significantly because of their propagation features. 0.1 mg/L chromium and 0.1 mg/L imazalil) the effect varied from indifferent to toxic according to algal species and season. At concentration of 0.1 mg/L chromium and imazalil the division of cells resumed within 1-2 days of intoxication. At concentrations of the toxicants over 0.05 mg/L for silver and over 1.0 mg/L for chromium and imazalil a total cell number and proportion of living cells decreased. Imazalil sulfate at concentration 1.0 mg/L was found to inhibit the division of cells and imparted to them anomalous increase in size and the formation of gigantic cells. Such state of algae was reversible: giant cells rapidly resumed their division after being transferred to a toxicant-free medium. At the concentration 3.0 mg/L chromium we observed both undividing and proliferating cells. At high toxicant concentrations (0.1 and 0.5 mg/L silver; 10.0 mg/L chromium; 5.0, 10.0 and 20.0 mg/L imazalil) cell division stimulation preceded the fast death of algal population and the small immature cells predominated in the beginning of the treatment. Only the high-level toxicant treatment caused photosynthetic efficiency reducing twice as compared to the control level. On the whole, the freshwater algae were found to be more sensitive to heavy metal action than marine algae. It was shown the existence of algostatic effect of silver after the growth of algal cultures in the presence of high toxicant concentrations. In this case the cell number stayed particularly unchangeable during the period of the experiment. S. quadricauda adaptation to extreme environmental pressure was analyzed by using an experimental model of the multiple intoxication (triple 10.0 mg/L chromium intoxication and double 1.0 mg/L silver intoxication). The selection of the resistant algal cells in the presence of high toxicant concentrations was demonstrated. These cells could restore the algal population. It is concluded that there are initial resistant cell number within the heterogenous algal population is 3-7 % (depending on toxicant) of initial cell number. A modified fluctuation analysis was performed to distinguish resistant cells within S. quadricauda and T. weissflogii laboratory cultures that had originated as a result of random spontaneous pre-selective mutations (prior to chromium exposure) from those arising through acquired post-selective adaptation (during the exposure to chromium). The changes of population structure of freshwater green alga S. quadricauda and marine diatom alga T. weissflogii were studied under different regimens of chromium exposure. Data on the cell number, their photosynthetic characteristics, population structure and share of alive and dead cells will be appropriate for use to predict the most sensitive ecosystem responses and indicate the permissible amount of toxicants in the environment. These data may have important implications for design and interpretations of the bioassay, especially within the context of the hazard/risk assessment.At low metal concentrations (0.0001, 0.001 and 0.01 mg/L) and low pesticide concentration (0.001 mg/L) the total cell number decreased as compare to the control one. The reason of possible population growth delay under low-level toxic exposure was the arrest of proliferation of some cells (probably, the most sensitive cells within heterogeneous population) rather than cell cycle slowdown in all cells. Notice, that the differences between control and sample cultures at low concentrations were reversible during the period of experiment. At medium toxicant concentrations (0.05 mg/L silver,0.1 mg/L chromium and 0.1 mg/L imazalil) the effect varied from indifferent to toxic according to algal species and season. At concentration of 0.1 mg/L chromium and imazalil the division of cells resumed within 1-2 days of intoxication. At concentrations of the toxicants over 0.05 mg/L for silver and over 1.0 mg/L for chromium and imazalil a total cell number and proportion of living cells decreased. Imazalil sulfate at concentration 1.0 mg/L was found to inhibit the division of cells and imparted to them anomalous increase in size and the formation of gigantic cells. Such state of algae was reversible: giant cells rapidly resumed their division after being transferred to a toxicant-free medium. At the concentration 3.0 mg/L chromium we observed both undividing and proliferating cells. At high toxicant concentrations (0.1 and 0.5 mg/L silver; 10.0 mg/L chromium; 5.0, 10.0 and 20.0 mg/L imazalil) cell division stimulation preceded the fast death of algal population and the small immature cells predominated in the beginning of the treatment. Only the high-level toxicant treatment caused photosynthetic efficiency reducing twice as compared to the control level. On the whole, the freshwater algae were found to be more sensitive to heavy metal action than marine algae. It was shown the existence of algostatic effect of silver after the growth of algal cultures in the presence of high toxicant concentrations. In this case the cell number stayed particularly unchangeable during the period of the experiment. S. quadricauda adaptation to extreme environmental pressure was analyzed by using an experimental model of the multiple intoxication (triple 10.0 mg/L chromium intoxication and double 1.0 mg/L silver intoxication). The selection of the resistant algal cells in the presence of high toxicant concentrations was demonstrated. These cells could restore the algal population. It is concluded that there are initial resistant cell number within the heterogenous algal population is 3-7 % (depending on toxicant) of initial cell number. A modified fluctuation analysis was performed to distinguish resistant cells within S. quadricauda and T. weissflogii laboratory cultures that had originated as a result of random spontaneous pre-selective mutations (prior to chromium exposure) from those arising through acquired post-selective adaptation (during the exposure to chromium). The changes of population structure of freshwater green alga S. quadricauda and marine diatom alga T. weissflogii were studied under different regimens of chromium exposure. Data on the cell number, their photosynthetic characteristics, population structure and share of alive and dead cells will be appropriate for use to predict the most sensitive ecosystem responses and indicate the permissible amount of toxicants in the environment. These data may have important implications for design and interpretations of the bioassay, especially within the context of the hazard/risk assessment.
Invasion by introduced species cause huge environmental damage and economic (estimated in $138 billion in USA). Marine ecosystems are specially affected by introduced species of toxin-producing microalgae. Ships ballast water has been considered the major vector in dispersion of phytoplankton. However, most ships do not use ballast water. Alternatively, we propose that the biofouling recovering the underwater body of ships is the main cause of microalgal dispersion. Antifouling paints (containing tributyltin, TBT or other toxics) are used to coat the bottoms of ships to prevent biofouling. After sampling biofouling recovering the underwater body of ships we demonstrate that numerous coastal, oceanic and toxin-producing microalgae species proliferates attached on bottoms of ships directly on TBT antifouling paint. These microalgae species should be resistant variants because antifouling paints rapidly destroy sensitive wild type microalgae. Consequently, the key to explain microalgae species transport via ships biofouling is know the mechanisms that allow to these species to survive long time attached to antifouling paint. A fluctuation analysis demonstrate that genetic adaptation by rare spontaneous mutation, which occurs by chance prior to antifouling exposure is the mechanism allowing adaptation of microalgae to antifoulig paints and their dispersion in the ships biofouling. Around 3 TBT-resistant mutants per each 10-4 wild type sensitive cells occurs in microalgal population. This assures a rapid colonization of ships bottoms to travel long-distances.
A thermotolerant Desmid was isolated from Tunisian geothermal spring (Ain-Echfa) in the region of Korbous northeast of Tunisia. Under light microscope, this alga was identified as belonging to the genus Cosmarium. Combined effect of light intensity and temperature on biochemical composition (carbohydrate, lipid and protein) of this strain was evaluated using a 3 2 factorial design. This design was carried out with light levels of 20, 70, and 120 µmol photons m-2 s-1 and temperature of 15, 30 and 45 °C. Our findings revealed that, at the stationary stage, the major compound of Cosmarium sp was the carbohydrate with a maximum of 81.8%. Statistical analysis demonstrated that biochemical composition of this strain was mainly influenced by light intensity. The experimental design showed that, the highest levels of protein, carbohydrate and lipid were obtained at the lowest light intensity (20 μmol photons m −2 s −1).
Marine ecosystems are affected by introduced species including microalgae. We propose that biofouling on ships’ hulls is a potentially important mechanism for microalgae dispersal worldwide. Biofouling samples, for phytoplankton composition analysis, were collected in Spanish Mediterranean ports from the hulls of ships that had completed oceanic journeys from other Mediterranean ports, and long journeys from the Atlantic and Indian Oceans. Samples representing the local population of phytoplankton either in the water column or attached to the biofouling of locally-based ship-hulls were used as controls. A broad variety of microalgae species (including toxic dinoflagellates), which were not present in the local phytoplankton populations were found on the biofouling film of the ships that had been on distant journeys. In spite of the presence of the antifouling paints containing toxic compounds, microalgae were able to rapidly adapt to these non-favourable conditions. Consequently, our study shows that ships’ biofouling seems to be a powerful vector for microalgae dispersal at a global scale due to the capacity of microalgae to attach to the biofouling film and to cope by adaptation mechanisms with antifouling compounds.
Los Baños de Vilo (S Spain) is a natural spa characterized by extreme sulphureous waters; however, populations of chlorophyceans inhabit in the spa. The adaptation mechanisms allowing resistance by photosynthetic microorganisms to the extreme sulphureous waters were studied by using a modified Luria–Delbrück fluctuation analysis. For this purpose, the adaptation of the chlorophycean Dictyosphaerium chlorelloides and the cyanobacterium Microcystis aeruginosa (both isolated from non-sulphureous water) were analysed in order to distinguish between physiological adaptation (acclimation) and genetic adaptation by the selection of rare spontaneous mutations. Acclimation to the extreme water was achieved by D. chlorelloides; however, M. aeruginosa cells proliferated as a consequence of selection of favoured mutants (i.e. genetic adaptation). The resistant cells of M. aeruginosa appeared with a frequency of 7.1×10−7 per cell per generation, and the frequency of the resistant allele, under non-selective conditions, was estimated to be 1.1×10−6 per cells as a consequence of the balance mutation–selection. It could be hypothesized that the populations of eukaryotic algae living in the Los Baños de Vilo could be the descendants of chlorophyceans that arrived fortuitously at the spa in the past. On the other hand, cyanobacteria could quickly adapt by the selection of favoured mutants. The single mutation that allows resistance to sulphureous water from Baños de Vilo in M. aeruginosa represents a phenotypic burden impairing growth rate and photosynthetic performance. The resistant-variant cells of M. aeruginosa showed a lower acclimated growth rate and a decreased maximum quantum yield and photosynthetic efficiency, in comparison to the wild-type cells.
Algae have been observed in many different extreme environments. We conducted a taxonomic diatom survey from Ice Pond Run stream, Friendship Hills National Historic Site, Fayette County, Pennsylvania in 2002. This stream is chronically impacted by acid mine drainage. The pH observed was low and ranged from 1.91 to 2.22. We identified three algal genera and six species. Two species counted as Eunotia geitlerii and E. exigua showed to have frustule incised ventral deformity and addition of extra striae, which represented 13% of the community relative percentage. Pinnularia subcapitata also showed highly silicified punctae with shallow pores.
There is increasing scientific interest in how phytoplankton reacts to petroleum contamination, since crude oil and its derivatives are generating extensive contamination of aquatic environments. However, toxic effects of short-term petroleum exposure are more widely known than the adaptation of phytoplankton to long-term petroleum exposure. An analysis of short-term and long-term effects of petroleum exposure was done using experimental populations of freshwater (Scenedesmus intermedius and Microcystis aeruginosa) and marine (Dunaliella tertiolecta) microalgae isolated from pristine sites without crude oil product contamination. These strains were exposed to increased levels of petroleum and diesel oil. Short-term exposure to petroleum or diesel oil revealed a rapid inhibition of photosynthetic performance and cell proliferation in freshwater and marine phytoplankton species. A broad degree of inter-specific variation in lethal contamination level was observed. When different strains were exposed to petroleum or diesel oil over the long-term, the cultures showed massive destruction of the sensitive cells. Nonetheless, after further incubation, some cultures were able to grow again due to cells that were resistant to the toxins. By means of a fluctuation analysis, discrimination between cells that had become resistant due to physiological acclimatization and resistant cells arising from rare spontaneous mutations was accomplished. In addition, an analysis was done as to the maximum capacity of adaptation to a gradual contamination process. An experimental ratchet protocol was used, which maintains a strong selection pressure in a temporal scale up to several months over very large experimental populations of microalgae. Microalgae are able to survive to petroleum contamination as a result of physiological acclimatization without genetic changes. However, when petroleum concentration exceeds the physiological limits, survival depends exclusively on the occurrence on mutations that confer resistance and subsequent selection of these mutants. Finally, it is certain that further mutations and selection will ultimately determine adaptation of microalgae to the environmental forcing.
In order to study adaptation of microalgae to petroleum contamination, we have examined an environmental stress gradient by crude oil contamination in the Arroyo Minero River (AMR), Argentina. Underground crude oil has constantly leaked out since 1915 as a consequence of test drilling for possible petroleum exploitation. Numerous microalgae species proliferated in AMR upstream of the crude oil spill. In contrast, only four microalgal species were detected in the crude oil spill area. Species richness increases again downstream. Microalgae biomass in the crude oil spill area is dominated by a mesophile species, Scenedesmus sp. Effects of oil samples from AMR spill on photosynthetic performance and growth were studied using laboratory cultures of two Scenedesmus sp. strains. One strain (Se-co) was isolated from the crude oil spill area. The other strain (Se-pr) was isolated from a pristine area without petroleum contamination. Crude oil has undetectable effects on Se-co strain. In contrast crude oil rapidly destroys Se-pr strain. However, Se-pr strain can adapt to low doses of petroleum (≤ 3% v/v total hydrocarbons/water) by means of physiological acclimatization. In contrast, only rare crude oil-resistant mutants are able to grow under high levels of crude oil (≥ 10% v/v total hydrocarbons/water). These crude oil-resistant mutants have arisen through rare spontaneous mutations that occur prior to crude oil exposure. Species richness in different areas of AMR is closely connected to the kind of mechanism (genetic adaptation vs. physiological acclimatization) that allows adaptation. Resistant-mutants are enough to assure the survival of microalgal species under catastrophic crude oil spill.
In November 2002, the oil tanker Prestige sank off the northwestern coast of Spain, spilling more than 50,000 tons of petroleum with disastrous ecological and economical consequences. In order to analyse the harmful consequences of the oil spill on marine microalgae, short- and long-term effects of oil samples from the Prestige spill were studied using laboratory cultures of Dunaliella tertiolecta (strain Dt1Lwt). Significant inhibition of photosynthesis (assessed by F(v)/F(m), ETR(max) and alpha estimations) was observed after only 1h of oil exposure with clear concentration dependency. Three days later, photosynthetic activity remained inhibited although cell survival was only slightly effected. In cultures exposed to the lowest oil concentration, mitotic rates and percentage of motile cells were 17-33% and 12-42% of the controls, respectively. After 1 month, neither dividing nor motile cells were observed at the highest oil concentrations. However, after further incubation, occasionally the growth of rare cells resistant to oil was found. A fluctuation analysis was carried out to distinguish between resistant cells arising from rare spontaneous mutations and resistant cells arising from physiological or other mechanisms of adaptation. The existence of rapid evolution as result of preselective mutations from petroleum sensitivity to petroleum resistance was observed. Resistant cells arose by rare spontaneous mutations prior to the addition of oil, with a mutation rate of 2.76x10(-5) oil-resistant mutants per cell division. Apparently, rare spontaneous preselective mutations are able to assure the survival of microalgae in oil-polluted environments.
Los resultados del análisis de fluctuación descrito por Luria y delbrück sugieren que las cianobacterias y las microalgas clorofíceas son capaces de adaptarse a concentraciones letales de sustancias tóxicas de origen antropogénico a través de mutaciones preadaptativas y preselectivas que suceden al azar antes de que las células entren en contacto con la sustancia tóxica. Los contaminantes testados fueron los herbicidas glifosate, simazina y diquat, el antibiotico cloranfenicol, los contaminantes industriales formaldehído y DEAB, y el metal pesado Cr(VI). Las células de fitoplancton resistentes, incubadas en la sustancia a la que son resistentes, evolucionan gracias a procesos de mutación-selección aumentando la tasa de división y el rendimiento cuántico de la fotosíntesis. Además los resultados de los trabajos experimentales indican que las mutaciones espontáneas preadaptativas son capaces de asegurar la adaptación instantánea de determinadas clorofíceas mesófilas a ambientes naturales extremos, como aguas con sustancias tóxicas de origen volcánico procedente la Isla de Vulcano (Italia), y aguas ácidas con una elevada concentración de metales pesados del Arroyo de Aguas Agrias en Tharsis (Huelva) y Mynyyd Parys (País de Gales). Por último, proponemos el uso simultáneo de cepas de clorofíceas sensibles y resistentes a un determinado agente tóxico para la construcción de biosensores sensibles y específicos.
Desde 1969, en el Parque Nacional de Doñana y su entorno se han descrito 13 mortandades en masa de fauna salvaje cuyas causas no han sido establecidas con suficiente rigor científico. Era necesario y urgente, por lo tanto, el conocer las causas de esos eventos de mortandad considerando la extraordinaria importancia ecológica de Doñana como santuario de numerosas especies amenazadas. Por lo tanto, el objeto y justificación de esta tesis es, precisamente, investigar el origen de las mortandades en masa descritas y proponer métodos sencillos de estudio y predicción de aparición de cianobacterias tóxicas en las marismas. Los resultados muestran que las proliferaciones de cianobacterias son eventos frecuentes en las marismas de Doñana y las cianotoxinas están claramente relacionadas con al menos buena parte de las mortandades de fauna salvaje que se producen. En esta tesis también se propone un protocolo de alerta temprana para la detección de cianobacterias tóxicas en áreas protegidas.
Estamos en un periodo de extinción global consecuencia de las actividades humanas y que están alterando los procesos de la biasfera. Las poblaciones de microalgas estan siendo expuestas por primera vez a estos productos fruto de la actividad antropagénica y sus mecanismos de adaptación son muy poco conocidos. Las cianobacterias y microalgas pueden adaptarse a nuevas condiciones ambientales a través de mutaciones espontáneas o a través de respuestas individuales (p.e. los organismos resistentes se pueden producir por mutaciones que ocurren antes de la exposición al agente selectivo, o por una respuesta especifica y directa al contaminante). Nosotros hemos trabajado en los mecanismos de adaptación de estos organismos al cambio ambiental brusco debido a contaminantes del agua. El análisis de fluctuación es el procedimiento adecuado para el estudio del proceso adaptativo. Las especies de cianobacterias y microalgas expuestas a distintos contaminantes (herbícidas, antibióticos, metales pesados, aguas sulfurosas y otros .. .) muestran variantes resistentes que se producen por raras mutaciones espontáneas que ocurren antes de la exposición al contaminante. Estos mutantes resistentes mostraron una disminución del crecimiento y de la fotosíntesis respecto a la población sensible. Las mutaciones espontáneas pueden ser suficientes para asegurar la adaptación en las enormes poblaciones de microalgas.
Anthropogenic water pollution is producing a challenge to the survival of phytoplankton populations. From an ecological point of view, the tolerance of these microorganisms to water pollution is of paramount importance since they are the principal primary producers of aquatic ecosystems. The adaptation of a common chlorophyta species (Scenedesmus intermedius) exposed to selected dose-response chloramphenicol (CAP) concentrations has been analyzed. A fluctuation analysis demonstrated that CAP-resistant cells arise due to spontaneous mutation which occurs randomly prior to the antibiotic exposure. CAP-inhibited growth and photosynthetic performance of algal cells at 0.28 mg/l, and the IC(50(72)) value was established in 0.10 mg/l for both parameters. The mutation rate from CAP sensitivity to resistance was 1.01 x 10(-5) mutations per cell division, while the frequency of CAP-resistant allele in non-polluted environment was estimated to be 5.5 CAP-resistant mutants per 10(3) sensitive-cells. These results demonstrate that resistant mutants exhibit a diminished fitness until 5 mg/l of CAP, thus enabling the survival of microalgae population.
Traditionally, morphometrical traits are used to classify cyanobacteria. However, neither the importance of genetic factors in morphological variability nor genetic correlations between different morphometrical traits are known. Six morphometrical traits of individual cells and six morphometrical traits of colonies have been measured in 21 strains of Microcystis aeruginosa. A fixed model and a mixed model allowing genetic relationships between traits were both used to estimate genetic and residual correlations, and genetic variance/total phenotypic variance ratios Were used to estimate the 12 morphornetrical traits. Results showed that (1) colony size has a low genetic correlation with traits of individual cells (2) traits measured oil individual cells present a higher genetic variance/total phenotypic variance ratio than the corresponding trait in colonies and (3) genetic correlations between directly measured traits (maximal diameter and axis, minimal diameter and axis. perimeter, and Surface) are so high that they may be considered different expressions of the same underlying trait, namely size, so any one of them could be used without significant loss of information, instead of all of them. Fixed and mixed models showed the same conclusions, although mixed models preferably Should be used because they take into account the common random genetic basis of traits. Maximal cell diameter was used as a discriminator trait for Studying morphological differences between strains from different origins. Results suggest that environment may modulate strain mixtures in Microcystis populations.
The toxic spill of acid wastes rich in heavy metals/metalloids (AWHM) from the Aznalcóllar mine in April 1998, threatening the Doñana National Park, is considered to be the worst environmental disaster related to acute pollution in Spanish history. The aim of this work was to study the adaptation of microalgae (which play an important role as primary producers) from AWHM sensitivity to AWHM resistance by using the alga Scenedesmus intermedius as an experimental model. The Malthusian parameter (m) and the carrying capacity (K) were reduced by mud and soil samples collected from the affected area. A dose–effect analysis showed that fitness progressively diminished with increasing sample concentration. A fluctuation analysis demonstrated that AWHM-resistant cells arose by rare spontaneous mutations that occurred randomly prior to the incorporation of the AWHM. The rate of spontaneous mutation from AWHM sensitivity to AWHM resistance was 2·12×10 mutants per cell division. A competition experiment between wild-type AWHM-sensitive cells and AWHM-resistant mutants showed that in small populations the AWHM-resistant mutants are driven to extinction in the absence of selection for AWHM resistance. The resistant phenotypes are maintained in the absence of AWHM as the result of a balance between spontaneous mutation and natural selection, so that about 43 AWHM-resistant mutants per million cells are present in the absence of AWHM. Our experimental model suggests that mutation is essential for adaptation of microalgal populations to environmental changes. Rare spontaneous pre-adaptive mutation is enough to ensure the survival of microalgal populations in contaminated environments when the population size is large enough.
We argue that the mode of reproduction of microorganisms in nature can only be decided by population genetic information. The evidence available indicates that many parasitic protozoa and unicellular fungi have clonal rather than sexual population structures, which has major consequences for medical research and practice. Plasmodium falciparum, the agent of malaria, is a special case: the scarce evidence available is contradictory, some suggesting that uniparental lineages may exist in nature. This is puzzling (because P. falciparum is known to have a sexual stage) and poses a challenge that can be readily settled by ascertaining the frequency distribution of genotypes in natural populations.
There is increasing awareness of the need to evaluate the effects of contaminants at the population level. Genetic techniques offer a powerful approach to assess contaminant-induced changes in populations. Yet studies to date are relatively few and not always carefully designed to maximize the utility inherent in this approach. We present a summary of contemporary genetic assessment methods and a review of published studies of genetic effects in field-exposed aquatic organisms. We discuss evaluations of genetic patterns that use genetic adaptation, allozyme variation, and molecular genetic (DNA) variation. Direct tests of genetic adaptation are very effective in establishing a concrete, and potentially deleterious population-level effect of contaminant exposure, but they are difficult to accomplish with most field-exposed organisms. Allozyme surveys are relatively simple and common, and may provide data that are suggestive of contaminant effects. However, these are rarely conclusive, primarily because few allozyme loci are variable and these few loci represent extremely small portions of the genome. Molecular genetic techniques have the potential to be very effective. But, there is a tendency to emphasize the power of the techniques, rather than the underlying causes of the molecular genetic patterns observed. The strength of the conclusions of each study varies widely, partially derived from variation in the strength of the techniques. We caution that all these approaches are greatly improved by careful experimental design that includes adequate numbers of reference and contaminated sites and sample size. In addition, careful exposure assessment is required, including site and tissue chemistry, biomarker responses, and measures of potentially deleterious effects, such as DNA damage, or reduced reproductive output or survival.
The Rio Tinto, known by the Phoenicians as 'Ur-yero', or 'River of Fire', because of its deep red colour and high acidity, flows through the world's largest pyritic belt in southwestern Spain. Surprisingly, eukaryotic microbes are the principal contributors of biomass in this hostile river, which has a pH of 2 and contains much higher concentrations of heavy metals than are typically found in fresh waters. Here we show that the Rio Tinto shows an unexpected degree of eukaryotic diversity and includes new lineages that we have identified by sequence analysis of genes encoding small-subunit ribosomal RNAs. The diversity of these eukaryotes is much greater than that of prokaryotes, whose metabolism is responsible for the extreme environment.
Modern chemical residues from water pollution (such as herbicides, antibiotics and even chemical substances of military use) are a challenge to survival of microalgal populations. Adaptation of three microalgal species – Pseudanabaena planctonica (Cyanophyceae), Dunaliella tertiolecta (Polyblepharidaceae, Chlorophyceae) and Scenedesmus sp. (Chlorophyceae) – to growth and survival in the presence of erythromycin, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and 2,4,6-trinitrotoluene was analysed as an experimental model. Growth of these species was restricted even by micromolar concentrations of such xenobiotics. When such contaminants are added to a dense microalgal culture, the cell density will be reduced after a few days due to the death of sensitive cells. However, after further incubation for several days, the culture will sometimes increase in density again due to the growth of a cell variant which is resistant to the contaminants. A Luria–Delbrück fluctuation analysis was carried out to distinguish between resistant cells arising from rare spontaneous mutation and resistant cells arising from other mechanisms of adaptation. In all cases, the contaminant-resistant cells arise randomly by rare spontaneous mutation during replication of cells prior to the addition of the contaminant (pre-selective mutations). Since wild-type microalgal genotypes are unable to survive in the presence of such contaminants, spontaneous pre-selective mutation (i.e. mutation from herbicide sensitivity to herbicide resistance) offers insights into the evolutionary capabilities of microalgal populations in contaminated environments. The rate of spontaneous mutation from sensitivity to resistance ranged from 2.0 × 10⁻⁶ mutants per cell division for erythromycin sensitive→ erythromycinresistantP. planctonica to 8.2 × 10⁻⁶ mutants per cell division for TNTsensitive→ TNTresistantScenedesmus sp. Since contaminant-resistant mutants have a diminished fitness, the resistant variants are maintained in the absence of the contaminants as the result of balance between new resistant cells arising from spontaneous mutation and resistant cells eliminated by natural selection. Thus recurrence of rare spontaneous pre-selective mutations ensures the survival of microalgal population in suddenly polluted environments.
Chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant physiologists and ecophysiologists. This review aims to provide an introduction for the novice into the methodology and applications of chlorophyll fluorescence. After a brief introduction into the theoretical background of the technique, the methodology and some of the technical pitfalls that can be encountered are explained. A selection of examples is then used to illustrate the types of information that fluorescence can provide.
There is increasing evidence, from molecular to biogeographic scales, of how extreme environmental conditions lie behind much evolutionary change. While periods of severe stress may be unpredictable and even of short duration, fundamental taxonomic changes are likely at these times, in terms of both extinction and bursts of speciation. This book emphasises genetic changes in populations at the extreme ends of the stress gradient, at the limits of resistance. In some cases, stress acts as an "environmental probe'. Biological systems under stress can be described in terms of energetic costs, from which suggestive associations between habitat, life history characteristics and stress resistance emerge. Following an introduction which evaluates how stress might be defined, what responses might result from stress, and how to measure stress response, chapters are on: the evolutionary and ecological importance of environmental stress (looking at fossil extinction, acyclic climatic stress, species distributions, habitat classification and competition); stress and protein variation; genetic variation in stress response; effects of stress on genetic variation; general stress resistance; stress response, costs and trade-offs; and stress, species margins and conservation. -P.J.Jarvis
Stress is a difficult term to define in a biological context. The relevant meaning of the word given by the Shorter Oxford English Dictionary (1933) was “the over powering pressure of some adverse force or influence”. In science it was originally used in a purely mechanical sense, e.g. a “force acting on contiguous surfaces of a body and tending to disarrange its particles” (Beadnell 1942), which still remains an appropriate definition to apply to the operation of water movements on an algal thallus. A reasonable extension is to take “tending to disarrange its particles” as including alterations in physiological processes and metabolic patterns, so making it applicable generally to effects on the activities of living organisms.
Residues contribute to water pollution and pose a challenge to microalgal populations because numerous contaminants are toxic to microalgae, even in the micromolar range. Adaptation of microalgae from herbicide sensitivity to herbicide resistance was analysed by an ecological genetic approach, using the unicellular alga Dictyosphaerium chlorelloides (Chlorophyceae) as an experimental model. A dose-effect study showed that the Malthusian parameter under conditions of r selection in an uncrowded environment and the carrying capacity under conditions of K selection in an crowded environment were both restricted even by low concentrations (< 1 muM) of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) herbicide. When a culture was treated with 50 muM DCMU, it cleared after a few days, as a result of destruction of sensitive cells by the herbicide. However, after further incubation for several days, the culture sometimes regained colour, owing to the growth of cell variants resistant to the herbicide. A fluctuation analysis was carried out to distinguish between (1) herbicide-resistant cells arising by direct and specific acquired adaptation in response to the herbicide and (2) herbicide-resistant cells arising by rare spontaneous mutations occurring randomly during replication of organisms prior to the incorporation of the herbicide. The fluctuation analysis unequivocally demonstrated that DCMU is not facilitating the development of DCMU-resistant cells; rather, we found that DCMU-resistant cells occur spontaneously by mutation in nonselective conditions prior to the incorporation of the herbicide (preselective mutations). The rate of spontaneous mutation from DCMU sensitivity to DCMU resistance was similar to 2.2 X 10(-6) mutants per cell division. Mutation was recurrent from a normal wild-type DCMU-sensitive allele to an DCMU-resistant allele, but such herbicide-resistant alleles were detrimental in terms of fitness in the absence of the herbicide. A competition experiment between wild-type DCMU-sensitive cells and DCMU-resistant mutants showed that, in small populations, the DCMU-resistant mutants are driven to extinction. The resistant variants are maintained in the absence of the herbicide as the result of a balance between new resistant cells arising by rare spontaneous mutation and resistant cells eliminated by natural selection. In our case, the average frequency of DCMU-resistant mutants in the absence of the DCMU is about five DCMU-resistant mutants per million cells. The results of our experimental model suggest that spontaneous mutation from herbicide sensitivity to herbicide resistance is sufficient in itself to assure the survival of microalgae populations in herbicide-contaminated environments when the population size is large.
Modern chemical residues from water pollution (such as herbicides, antibiotics and even chemical substances of military use) are a challenge to survival of microalgal populations. Adaptation of three microalgal species to growth and survival in the presence of erythromycin, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and 2,4,6-trinitrotoluene was analysed as an experimental model. Growth of these species was restricted even by micromolar concentrations of such xenobiotics. When such contaminants are added to a dense microalgal culture, the cell density will be reduced after a few days due to the death of sensitive cells. However, after further incubation for several days, the culture will sometimes increase in density again due to the growth of a cell variant which is resistant to the contaminants. A Luria6 mutants per cell division for erythromycin sensitive [longrightarrow A: long right arrow] erythromycinresistant P.planctonica to 8·2×10−6 mutants per cell division for TNTsensitive [longrightarrow A: long right arrow] TNTresistant Scenedesmus sp. Since contaminant-resistant mutants have a diminished fitness, the resistant variants are maintained in the absence of the contaminants as the result of balance between new resistant cells arising from spontaneous mutation and resistant cells eliminated by natural selection. Thus recurrence of rare spontaneous pre-selective mutations ensures the survival of microalgal population in suddenly polluted environments.
In the past, ecophysiologically oriented photosynthesis research has been governed by gas-exchange measurements, mainly involving sophisticated (and costly) systems for simultaneous detection of CO2 uptake and H2O evaporation (see, e.g., Field et al. 1989). With the help of these methods, fundamental knowledge on in situ photosynthesis has been gained. Only recently, progress has been made in the development of alternative practical methods for nonintrusive assessment of in vivo photosynthesis which have the potential of not only evaluating overall quantum yield and capacity, but also allowing insights into the biochemical partial reactions and the partitioning of excitation energy (see, e.g., Snel and van Kooten 1990). As a consequence, photosynthesis research at the level of regulatory processes has been greatly stimulated, leading to important new concepts (see reviews by Foyer et al. 1990; Demmig-Adams 1990; Melis 1991; Allen 1992). In particular, chlorophyll fluorescence has evolved as a very useful and informative indicator for photosynthetic electron transport in intact leaves, algae, and isolated chloroplasts (reviews by Briantais et al. 1986; Renger and Schreiber 1986; Schreiber and Bilger 1987, 1992; Krause and Weis 1991; Karukstis 1991).
I present a bio‐optical model that estimates the internal self‐shading caused by absorbing matter in planktonic organisms as well as the specific benefit afforded by the accumulation of sunscreen compounds. The model is applied to the examination of case studies of sunscreen‐bearing microorganisms and to the prediction of the effects of organismal size on both the inherent sensitivity to ultraviolet radiation and the possible amelioration of this condition by means of sunscreen accumulation. The model predicts that sunscreens cannot be used as a photoprotective mechanism of any relevance by picoplankters (cell radii, < 1 µ m), which are also the most inherently sensitive size‐class. Conversely, the microplankters (cell radii, 10−> 100 µ m) can use sunscreens with efficiencies comparable to well‐studied damage‐repair mechanisms. Among nanoplankters (cell radii, 1−< 10 µ m), sunscreens can afford considerable benefits but only at the expense of relatively heavy investments and with restricted efficiencies.
Since stress can be defined as anything which reduces growth or performance, it follows that, if appropriate genetic variability is present, classical evolutionary changes in populations are to be expected in any situation where a consistent stress is occurring. There is now considerable evidence for such evolution, producing constitutive adaptations in plants in response to stress, which are specific to the stress concerned. Stress may however operate in a temporary or fluctuating manner. In these situations, facultative adaptations, able to be produced within a single genotype through phenotypic plasticity, will be more appropriate. Very different specific phenotypic response systems, both morphological or physiological, can be found in plants in relation to different fluctuating stresses, operating over a wide range of time scales. These response systems are under normal genetic control and appear to be products of normal evolutionary processes. They can however have quite complex features, analogous to the behavioural response systems in animals.
The increasing rates of global extinction due to human activities necessitate studies of the ability of organisms to adapt to the new environmental conditions resulting from human disturbances. We investigated the evolutionary adaptation of a microalga to sudden environmental change resulting from exposure to novel toxic chemical residues. A laboratory strain of Dictyosphaerium chlorelloides (Naum.) Kom. and Perm. (Chlorophyceae) was exposed to increasing concentrations of the modern contaminant 2,4,6-trinitrotoluene (TNT). When algal cultures were exposed to 30 mg·L−† TNT, massive lysis of microalgal cells was observed. The key to understanding the evolution of microalgae in such a contaminated environment is to characterize the TNT-resistant variants that appear after the massive lysis of the TNT-sensitive cells. A fluctuation analysis demonstrated unequivocally that TNT did not facilitate the appearance of TNT-resistant cells; rather it was found that TNT-resistant cells appeared spontaneously by rare mutations under nonselective conditions, before exposure to TNT. The estimated mutation rate was 1.4 × 10−5 mutants per cell division. Isolated resistant mutants exhibited a diminished fitness in the absence of TNT. Moreover, the gross photosynthetic rate of TNT-resistant mutants was significantly lower than that of wild-type cells. Competition experiments between resistant mutants and wild-type cells showed that in small populations, the resistant mutants were driven to extinction. The balance between mutation rate and the rate of selective elimination determines the occurrence of about 36 TNT-resistant mutants per million cells in each generation. These scarce resistant mutants are the guarantee of potential for adaptation.
The study of spontaneous mutation rates in mammalian cells has been hampered by the lack of an alternative to the cumbersome Luria and Delbrück fluctuation test. A brief review of mathematical treatments of spontaneous mutagenesis, along with some of the limitations of the fluctuation test, is presented. A new experimental method and a simple mathematical model for deriving the spontaneous mutation rate are described. Data from the transgenic Chinese hamster G12 cell line growing at two different rates is analyzed according to this model. The results support the concept that, at least for growing cells, the spontaneous mutation rate is independent of the growth rate, and the mutant fraction increases in a linear fashion with the number of generations.
Intertidal seaweeds are periodically exposed to air where they experience a variety of potentially stressful environmental conditions, including nutrient limitation, high light, high and low temperature, desiccation, and osmotic stress. This paper considers the current understanding of stress tolerance in intertidal seaweeds and discusses ways in which future research could increase our understanding of the role of environmental factors in the ecology and physiology of these algae. We believe research is required in at least three areas. 1) Laboratory physiological studies have established that correlations exist between stress tolerance and the vertical distribution of species. However, little information is available on the importance of stress in determining community structure in nature. Field experiments are essential to relate the impact of single or multiple stresses on the survival, growth, and reproductive output of macroalgae. In paticular, it is necessary to clarify the role of sublethal stress in determining the outcome of competitive interactions. 2) With the exception of obvious lethal effects or damage associated with extreme environmental conditions, such as unusually hot and dry weather, it is difficult to evaluate the occurrence and severity of stress in natural populations of seaweeds. There is a need to develop molecular and biochemical markers specific for individual stresses or groups of stresses to allow the unambiguous and direct determination of stress in situ. 3) Despite the apparent importance of stress in intertidal seaweeds, we are largely ignorant of the mechanistic basis of tolerance. The application of currently available tools of molecular and cell biology to the investigation of stress-induced transcriptional and translational changes could enormously increase our understanding of both the sites of, and pathways involved in, stress tolerance. In summary, there are numerous unanswered fundamental questions about the stress tolerance of intertidal seaweeds, providing opportunities for research ranging from field ecology to molecular biology and biochemistry.
A theoretical treatment of light attenuation within phytoplankton suspensions, developed in a previous paper, has now been extended to certain non-spherical cells and colonies of diatoms, blue-green and green algae.
Procedures for calculating the mean absorption cross-section for randomly oriented cells or colonies with the shape of cylinders, prolate spheroids or oblate spheroids, are described. The mean absorption cross-sections at a series of wavelengths throughout the photosynthetic waveband are compared for model algae of various shapes, sizes and pigment compositions. The results clearly illustrate the principle that for a strongly absorbing algal cell/colony of a given volume, the more extended it is in space, the more effective it is as a light collector. The advantages of the more extended package are much less evident at wavelengths which are weakly absorbed.
For algae of a compact, e.g. spherical, shape a large cell or colony captures much less light (of a wavelength which is strongly absorbed) than an equivalent volume of smaller cells. However, it is also true that a large particle of very extended shape, e.g. a long thin cylinder, can capture as much light as a greater number of smaller particles (of the same total volume) of more compact shape. This means that for purposes of light collection an alga is almost as well off when organized into long multicellular filaments as it would be if separated into a large number of single cells.
Using the calculated values of mean absorption cross-section the relationship between phytoplankton canopy structure and attenuation of photosynthetically active radiation (PAR) has been further investigated. Calculated values for the spectral distribution of light intensity, the total transmitted quantum flux, the vertical attenuation coefficients, and the increments in vertical attenuation coefficient per unit algal concentration, are presented for various model non-scattering suspensions corresponding to common naturally-occurring algae. The possible effects of turbidity on light attenuation in such systems are discussed.
Preface to the third edition Part I. The Underwater Light Field: 1. Concepts of hydrologic optics 2. Incident solar radiation 3. Absorption of light within the aquatic medium 4. Scattering of light within the aquatic medium 5. Characterizing the underwater light field 6. The nature of the underwater light field 7. Remote sensing of the aquatic environment Part II. Photosynthesis in the Aquatic Environment: 8. The photosynthetic apparatus of aquatic plants 9. Light capture by aquatic plants 10. Photosynthesis as a function of the incident light 11. Photosynthesis in the aquatic environment 12. Ecological strategies References and author index Index to symbols Index to organisms Index to water bodies Subject index.
When properly determined, spontaneous mutation rates are a more accurate and biologically meaningful reflection of underlying mutagenic mechanisms than are mutant frequencies. Because bacteria grow exponentially and mutations arise stochastically, methods to estimate mutation rates depend on theoretical models that describe the distribution of mutant numbers among parallel cultures, as in the original Luria-Delbr]uck fluctuation analysis. An accurate determination of mutation rate depends on understanding the strengths and limitations of these methods, and how to design fluctuation assays to optimize a given method. In this paper we describe a number of methods to estimate mutation rates, give brief accounts of their derivations, and discuss how they behave under various experimental conditions.
Incluye bibliografía e índice
Incluye bibliografía e índice
Luria-Delbrück fluctuation tests for the determination of the spontaneous mutation rate to ouabain resistance incultured L5178Y mouse lymphoma cells gave values in the range 0.44 to 1.03 X 10(-7) mutants per cell per generation. Addition of very low, non-toxic, levels of EMS (0.1 mM) and MMS (0.012 mM) 30-48 h before plating in selective medium gave a highly significant increase in the number of ouabain-resistant mutants. Methods for the calculation of spontaneous and induced mutation rates are discussed and a method for the computation of induced mutation rates is described. It is suggested that the modified fluctuation test is a simpler and considerably more sensitive assay for mutagens than the conventional experimental design. Some of its limitations are discussed.
In terms of evolution and fitness, the most significant spontaneous mutation rate is likely to be that for the entire genome (or its nonfrivolous fraction). Information is now available to calculate this rate for several DNA-based haploid microbes, including bacteriophages with single- or double-stranded DNA, a bacterium, a yeast, and a filamentous fungus. Their genome sizes vary by approximately 6500-fold. Their average mutation rates per base pair vary by approximately 16,000-fold, whereas their mutation rates per genome vary by only approximately 2.5-fold, apparently randomly, around a mean value of 0.0033 per DNA replication. The average mutation rate per base pair is inversely proportional to genome size. Therefore, a nearly invariant microbial mutation rate appears to have evolved. Because this rate is uniform in such diverse organisms, it is likely to be determined by deep general forces, perhaps by a balance between the usually deleterious effects of mutation and the physiological costs of further reducing mutation rates.
It has been hypothesized that genomic fluidity is an important component of tumorigenesis. Previous studies described the relationship between tumorigenicity and one marker for genomic fluidity, gene amplification. In this report, these studies are extended with the rat liver epithelial cell lines to show that: (i) the amplification in these cells arises in a spontaneous fashion in the population (i.e., the variants detected are not preexisting in the population), and (ii) the rate of spontaneous amplification (mutation), as measured by Luria-Delbrück fluctuation analysis, is significantly lower in the nontumorigenic cells than in the tumorigenic cells. The rate was estimated by using the Po method and the method of means. The rate of spontaneous amplification of the gene encoding the multifunctional protein CAD (containing the enzymatic activities carbamoyl-phosphate synthase, aspartate transcarbamylase, and dihydroorotase) in the highly tumorigenic cells was significantly greater than that for the nontumorigenic cells, reaching almost 1 x 10(-4) events per cell per generation. The rate of this mutagenic event is high compared to the rate of point mutations usually reported in mammalian cells, and its potential contribution to the tumorigenic process will be discussed.
Nucleic acids are replicated with conspicuous fidelity. Infrequently, however, they undergo changes in sequence, and this process of change (mutation) generates the variability that allows evolution. As the result of studies of bacterial variation, it is now widely believed that mutations arise continuously and without any consideration for their utility. In this paper, we briefly review the source of this idea and then describe some experiments suggesting that cells may have mechanisms for choosing which mutations will occur.
The study of spontaneous mutation rates in mammalian cells has been hampered by the lack of an alternative to the cumbersome Luria and Delbrück fluctuation test. A brief review of mathematical treatments of spontaneous mutagenesis, along with some of the limitations of the fluctuation test, is presented. A new experimental method and a simple mathematical model for deriving the spontaneous mutation rate are described. Data from the transgenic Chinese hamster G12 cell line growing at two different rates is analyzed according to this model. The results support the concept that, at least for growing cells, the spontaneous mutation rate is independent of the growth rate, and the mutant fraction increases in a linear fashion with the number of generations.
Over the past quarter century, detailed genus- and species-level similarities in cellular morphology between described taxa of Precambrian microfossils and extant cyanobacteria have been noted and regarded as biologically and taxonomically significant by numerous workers world-wide. Such similarities are particularly well documented for members of the Oscillatoriaceae and Chroococcaceae, the two most abundant and widespread Precambrian cyanobacterial families. For species of two additional families, the Entophysalidaceae and Pleurocapsaceae, species-level morphologic similarities are supported by in-depth fossil-modern comparisons of environment, taphonomy, development, and behavior. Morphologically and probably physiologically as well, such cyanobacterial "living fossils" have exhibited an extraordinarily slow (hypobradytelic) rate of evolutionary change, evidently a result of the broad ecologic tolerance characteristic of many members of the group and a striking example of G. G. Simpson's [Simpson, G.G. (1944) Tempo and Mode in Evolution (Columbia Univ. Press, New York)] "rule of the survival of the relatively unspecialized." In both tempo and mode of evolution, much of the Precambrian history of life--that dominated by microscopic cyanobacteria and related prokaryotes--appears to have differed markedly from the more recent Phanerozoic evolution megascopic, horotelic, adaptationally specialized eukaryotes.
Rates of spontaneous mutation per genome as measured in the laboratory are remarkably similar within broad groups of organisms but differ strikingly among groups. Mutation rates in RNA viruses, whose genomes contain ca. 10(4) bases, are roughly 1 per genome per replication for lytic viruses and roughly 0.1 per genome per replication for retroviruses and a retrotransposon. Mutation rates in microbes with DNA-based chromosomes are close to 1/300 per genome per replication; in this group, therefore, rates per base pair vary inversely and hugely as genome sizes vary from 6 x 10(3) to 4 x 10(7) bases or base pairs. Mutation rates in higher eukaryotes are roughly 0.1-100 per genome per sexual generation but are currently indistinguishable from 1/300 per cell division per effective genome (which excludes the fraction of the genome in which most mutations are neutral). It is now possible to specify some of the evolutionary forces that shape these diverse mutation rates.
Chlorophyll fluorescence analysis has become one of the most powerful and widely used techniques available to plant physiologists
and ecophysiologists. This review aims to provide an introduction for the novice into the methodology and applications of
chlorophyll fluorescence. After a brief introduction into the theoretical background of the technique, the methodology and
some of the technical pitfalls that can be encountered are explained. A selection of examples is then used to illustrate the
types of information that fluorescence can provide.
Adaptive mutation is defined as a process that, during nonlethal selections, produces mutations that relieve the selective pressure whether or not other, nonselected mutations are also produced. Examples of adaptive mutation or related phenomena have been reported in bacteria and yeast but not yet outside of microorganisms. A decade of research on adaptive mutation has revealed mechanisms that may increase mutation rates under adverse conditions. This article focuses on mechanisms that produce adaptive mutations in one strain of Escherichia coli, FC40. These mechanisms include recombination-induced DNA replication, the placement of genes on a conjugal plasmid, and a transient mutator state. The implications of these various phenomena for adaptive evolution in microorganisms are discussed.
Natural selection can adjust the rate of mutation in a population by acting on allelic variation affecting processes of DNA replication and repair. Because mutation is the ultimate source of the genetic variation required for adaptation, it can be appealing to suppose that the genomic mutation rate is adjusted to a level that best promotes adaptation. Most mutations with phenotypic effects are harmful, however, and thus there is relentless selection within populations for lower genomic mutation rates. Selection on beneficial mutations can counter this effect by favoring alleles that raise the mutation rate, but the effect of beneficial mutations on the genomic mutation rate is extremely sensitive to recombination and is unlikely to be important in sexual populations. In contrast, high genomic mutation rates can evolve in asexual populations under the influence of beneficial mutations, but this phenomenon is probably of limited adaptive significance and represents, at best, a temporary reprieve from the continual selection pressure to reduce mutation. The physiological cost of reducing mutation below the low level observed in most populations may be the most important factor in setting the genomic mutation rate in sexual and asexual systems, regardless of the benefits of mutation in producing new adaptive variation. Maintenance of mutation rates higher than the minimum set by this "cost of fidelity" is likely only under special circumstances.
Freshwater toxic cyanobacteria are an increasing problem to human and animal health. Control of cyanobacteria in water supply reservoirs involves the use of algaecides, such as copper sulphate, usually in a repetitive way. Repercussions of recurrent algaecide treatments on cyanobacteria population dynamics remain still unknown. We studied the adaptation of cyanobacteria to lethal doses of copper sulphate by using Microcystis aeruginosa as an experimental model. A fluctuation analysis demonstrated that copper-resistant cells arise by spontaneous mutations that occur randomly prior to exposition to copper sulphate. The rate of spontaneous mutation from copper sensitivity to resistance was 1.76 x 10(-6) mutants per cell division. Resistant mutants exhibited a diminished fitness in the absence of copper sulphate, but only these variants were able to grow at Cu(2+) concentrations higher than 5.8 microM. In addition, copper-resistant cells were significantly smaller than wild-type ones. Warnings on the long-term consequences of repetitive algaecide treatments in water supplies are suggested.
- L E Graham
- L W Wilcox
Graham LE, Wilcox LW. 2000. Algae. Upper Saddle River, NJ, USA:
Prentice Hall.
Precision of test methods. I. Guide for the Determination of Repeatability and Reproducibility for a Standard Test Method for Inter-Laboratory Tests. BS 5497. Part I
- British Standards Institute
British Standards Institute. 1979. Precision of test methods. I. Guide for the
Determination of Repeatability and Reproducibility for a Standard Test
Method for Inter-Laboratory Tests. BS 5497. Part I. London, UK: British
Standards Institute.
Algal Adaptation to Environmental Stresses. Physiological, Biochemical and Molecular Mechanisms
- G E Fogg
Fogg GE. 2001. Algal adaptation to stress-some general remarks. In:
Rai LC, Gaur JP, eds. Algal Adaptation to Environmental Stresses.
Physiological, Biochemical and Molecular Mechanisms. Berlin, Germany:
Springer, 1-20.
Analysis of polygenic traits ofMicrocystis aeruginosa(Cyanobacteria) strains by Restricted Maximum Likelihood (REML) procedures: 1. Size and shape of colonies and cells
- Ricom Altamiranom López-Rodasv Costase