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Zinc Sorption to Three Gram-Negative Bacteria: Combined Titration, Modeling, and EXAFS Study
Abstract
The acid-base and Zn sorption properties of three bacteria, Cupriavidus metallidurans CH34, Pseudomonas putida ATCC12633, and Escherichia coli K12DH5alpha, were investigated through an original combination of extended X-ray absorption fine structure (EXAFS) spectroscopy and equilibrium titration studies. Acid-base titration curves of the three strains were fitted with a model accounting for three conceptual reactive sites: an acidic (carboxyl and/or phosphodiester), a neutral (phosphomonoester), and a basic (amine and/or hydroxyl) group. Calculated proton and Zn equilibrium constants and site densities compare with literature data. The nature of Zn binding sites was studied by EXAFS spectroscopy. Phosphoester, carboxyl, and unexpectedly sulfhydryl ligands were identified. Their proportions depended on Zn loading and bacterial strain and were consistent with the titration results. These findings were compared to the structure and site density of the major cell wall components. It appeared that the cumulated theoretical site density of these structures (<2 Zn nm(-2)) was much lower than the total site density of the investigated strains (16-56 Zn nm(-2)). These results suggest a dominant role of extracellular polymeric substances in Zn retention processes, although Zn binding to inner cell components cannot be excluded.
... Compared to carboxyl and phosphoryl sites, sulfhydryl sites on bacterial cell surfaces are generally less abundant , but they form much stronger bonds with chalcophile metals such as Hg, Cd, Zn, Cu and Au (Yu and Fein, 2015;Nell and Fein, 2017;Yu and Fein, 2017b), resulting in the dominance of sulfhydryl sites in the adsorption of these metals onto bacterial cells under low metal loading conditions (Guine et al., 2006;Mishra et al., 2010;Pokrovsky et al., 2012;Yu and Fein, 2015). In addition, the concentration of sulfhydryl sites on bacterial cell surfaces can increase significantly as a function of growth conditions (Yu and Fein, 2017a), and hence sulfhydryl sites can contribute significantly to the adsorption of Cd, Hg and Au onto bacterial cells even under high metal loadings (Mishra et al., 2017;Yu and Fein, 2017b). ...
... The high concentration of sulfhydryl sites on the cell surface of P. putida leads to Cd-sulfhydryl binding representing a large proportion of the total adsorbed Cd budget under high Cd loading conditions (Table 1). Typically, because of the limited abundance of high affinity sulfhydryl binding sites on bacteria, metal-sulfhydryl binding decreases in importance when metal loadings exceed approximately 10 μmol/g (Guine et al., 2006;Mishra et al., 2010;Pokrovsky et al., 2012;Yu and Fein, 2015;Nell and Fein, 2017). However, our EXAFS analysis indicates that Cd-sulfhydryl binding represents over 50 % of the total adsorbed Cd budget in the early stationary phase biomass sample (Fig. S2, Table 1) which was exposed to a metal loading of approximately 130 μmol/g. ...
... Our experiments demonstrate that the extent of Cd toxicity to the bacterial cells is inversely related to the concentration of sulfhydryl sites on bacterial cell surfaces (Fig. 4b). In addition to Cd, the sulfhydryl sites on the cell surfaces of P. putida likely can reduce the toxicity of a range of other chalcophile or similar metals as well, such as Hg, Zn, Au and Cu, because these metals also strongly bind to sulfhydryl sites (Guine et al., 2006;Pokrovsky et al., 2012;Nell and Fein, 2017;Yu and Fein, 2017b). It is unclear at this time how widespread this detoxification strategy is among bacterial species, but sulfhydryl sites have been detected on the EPS molecules within the biofilms that are produced by some pathogenic bacteria (Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli) and biofilm formation bacteria on drinking water pipes (Pleomorphomonas oryza NM1 and Acidovorax ebreus NM25) (Lin et al., 2014), with the roles of their EPS sulfhydryl sites unexplored. ...
... The biomass of bacteria, fungi, yeasts and algae have been reported for effective and economical removal of a wide variety of toxic heavy metals from wastewater and engineering systems. Metal ions can be immobilized by functional groups such as carboxyls, phosphomonoesters, phosphodiesters, amines and hydroxyls that are native to the proteins, lipids, and carbohydrates on the cell walls of organisms [2]. A better understanding of how metal sorption takes place on the surfaces of microorganisms on molecular-scale is critical to elucidate the mechanisms involved in terms of mobility, speciation and bioavailability of metals in geological systems. ...
... Toner et al. [7] investigated Zn sorption by a bacterial biofilm of Pseudomonas putida at pH 6.9, and attributed zinc sorption to the biofilm predominantly to Zn-phosphoryl complexes, with a relatively small contribution from carboxyl-type complexes. Guiné et al. [2] reported sulfhydryl ligands were responsible for Zn adsorption to three Gram negative bacterial strains at low loadings of Zn. The above molecular-scale investigations demonstrated that sorption of heavy metals onto bacteria is controlled by carboxyl, phosphoryl and perhaps sulfhydryl functional groups on the cell wall of the microorganisms. ...
Cyanobacteria are promising biosorbent for heavy metals in bioremediation. Although sequestration
of metals by cyanobacteria is known, the actual mechanisms and ligands involved are not very well
understood. The binding characteristics of Cu(II) and Cd(II) by the cyanobacterium Spirulina platensis
were investigated using a combination of chemical modifications, batch adsorption experiments, Fourier
transform infrared (FTIR) spectroscopy and X-ray absorption fine structure (XAFS) spectroscopy. A significant
increase in Cu(II) and Cd(II) binding was observed in the range of pH 3.5–5.0. Dramatical decrease in
adsorption of Cu(II) and Cd(II) was observed after methanol esterification of the nonliving cells demonstrating
that carboxyl functional groups play an important role in the binding of metals by S. platensis. The
desorption rate of Cu(II) and Cd(II) from S. platensis surface was 72.7–80.7% and 53.7–58.0% by EDTA and
NH4NO3, respectively, indicating that ion exchange and complexation are the dominating mechanisms
for Cu(II) and Cd(II) adsorption. XAFS analysis provided further evidence on the inner-sphere complexation
of Cu by carboxyl ligands and showed that Cu is complexed by two 5-membered chelate rings on S.
platensis surface.
... Among the various reactive components associated with bacterial cell walls, bacterial extracellular polymeric substance (EPS) is of particular importance which affects biofilm formation and cell adhesion to solid substrates (Beveridge and Fyfe, 1985;Parikh and Chorover, 2006). Furthermore, these polymers potentially have a significant effect on the acid-base properties and metaladsorption characteristics of bacterial cells (Toner et al., 2005;Guiné et al., 2006). A small number of studies have investigated the proton and metal binding behavior of isolated EPS. ...
... It was reported by Liu and Fang (2002) that site concentrations of isolated EPS were 20-30-fold higher than those found on bacterial cells on a per gram basis. Guiné et al. (2006) found that the cumulated theoretical cell-wall site densities for three gram-negative bacterial strains were much lower than those necessary to explain the observed zinc loading, and suggested that the excess loading may be explained by the contribution made by EPS. Inner-sphere complexation of carboxyl and phosphate groups were extensively reported for heavy metals adsorption on the bacterial surface or isolated bacterial EPS (Kelly et al., 2002;Boyanov et al., 2003;Pal and Paul, 2008). ...
The effect of extracellular polymeric substances (EPS) of Gram-positive Bacillus subtilis and Gram-negative Pseudomonas putida on Cu(II) adsorption was investigated using a combination of batch adsorption, potentiometric titrations, Fourier transform infrared spectroscopy. Both the potentiometric titrations and the Cu(II) adsorption experiments indicated that the presence of EPS in a biomass sample significantly enhance Cu(II) adsorption capacity. Surface complexation modeling showed that the pK a values for the three functional groups (carboxyl, phosphate and hydroxyl) were very similar for untreated and EPS-free cells, indicating no qualitative difference in composition. However, site concentrations on the untreated cell surface were found to be significantly higher than those on the EPS-free cell surface. Infrared analysis provided supporting evidence and demonstrated that carboxyl and phosphate groups are responsible for Cu(II) adsorption on the native and EPS-free cells.
... Among the various reactive components associated with bacterial cell walls, bacterial extracellular polymeric substance (EPS) is of particular importance which affects biofilm formation and cell adhesion to solid substrates (Beveridge and Fyfe, 1985;Parikh and Chorover, 2006). Furthermore, these polymers potentially have a significant effect on the acidebase properties and metal-adsorption characteristics of bacterial cells (Toner et al., 2005;Guiné et al., 2006). A small number of studies have investigated the proton and metal binding behavior of isolated EPS. ...
... It was reported by Liu and Fang (2002) that site concentrations of isolated EPS were 20e30-fold higher than those found on bacterial cells on a per gram basis. Guiné et al. (2006) found that the accumulated theoretical cell-wall site densities for three Gram-negative bacterial . FTIR spectra in the 800e2000 cm À1 region of untreated and EPS-free P. putida cells before and after exposure to solutions with 40 mg L À1 Cd at pH 6.0. ...
The role of extracellular polymeric substances (EPS) in Cd adsorption by Bacillus subtilis and Pseudomonas putida was investigated using a combination of batch adsorption experiments, potentiometric titrations, Fourier transform infrared spectroscopy (FTIR). An increased adsorption capacity of Cd was observed for untreated bacteria relative to that for EPS-free bacteria. Surface complexation modeling of titration data showed the similar pK a values of functional groups (carboxyl, phosphate and hydroxyl) between untreated and EPS-free bacteria. However, site concentrations on the untreated bacteria were found to be higher than those on the EPS-free bacteria. FTIR spectra also showed that no significant difference in peak positions was observed between untreated and EPS-free bacteria and carboxyl and phosphate groups were responsible for Cd adsorption on bacterial cells. The information obtained in this study is of fundamental significance for understanding the interaction mechanisms between heavy metals and biofilms in natural environments.
... Toner et al. (2005) demonstrated the importance of phosphoryl and carboxyl binding sites for Zn in a bacterial biofilm at pH 7.0 and concluded that metal complexation by the EPS component was likely to be significant. Guiné et al. (2006) found that the cumulated theoretical cell-wall site densities for three gram-negative bacterial strains were much lower than those necessary to explain the observed zinc loading, and suggested that the excess loading may be explained by the contribution made by EPS. ...
... EPS, minerals and their composites exhibited substantial buffering behavior and weak inflection points on the titration curves indicate the deprotonation of different functional groups (Fig. 2). Surface functional groups are the basic units of surface complexation reactions on organism or minerals (Wei and Wu, 2000;Guiné et al., 2006). The deprotonation of a functional group can be represented by the following generic reaction (Borrok and Fein, 2004): ...
Equilibrium adsorption experiments, isothermal titration calorimetry and potentiometric titration techniques
were employed to investigate the adsorption of Cu(II) by extracellular polymeric substances (EPS)
extracted from Pseudomonas putida X4, minerals (montmorillonite and goethite) and their composites.
Compared with predicted values of Cu(II) adsorption on composites, the measured values of Cu(II) on
EPS-montmorillonite composite increased, however, those on EPS-goethite composite decreased. Potentiometric
titration results also showed that more surface sites were observed on EPS-montmorillonite
composite and less reactive sites were found on EPS-goethite composite. The adsorption of Cu(II) on
EPS molecules and their composites with minerals was an endothermic reaction, while that on minerals
was exothermic. The positive values of enthalpy change (DH) and entropy change (DS) for Cu(II) adsorption
on EPS and mineral-EPS composites indicated that Cu(II) mainly interacts with carboxyl and phosphoryl
groups as inner-sphere complexes on EPS molecules and their composites with minerals.
... Bioremediation is a convenient and ecofriendly option that can be used to restore the contaminated environment by removing toxic metals from the environment [224,229]. Bioremediation of toxicants can be done by adsorption [230][231][232], physio-biochemical mechanisms [233][234][235][236], and molecular mechanisms [237][238][239]. Several enzymes (superoxide dismutase, SOD; catalase, CAT; glutathione S transferase, GST) and nonenzymatic compounds (reduced glutathione, GSH) play a key role in sustaining the ROS balance by detoxification (Figure 2). ...
Heavy metals, the most potent contaminants of the environment, are discharged into the aquatic ecosystems through the effluents of several industries, resulting in serious aquatic pollution. This type of severe heavy metal contamination in aquaculture systems has attracted great attention throughout the world. These toxic heavy metals are transmitted into the food chain through their bioaccumulation in different tissues of aquatic species and have aroused serious public health concerns. Heavy metal toxicity negatively affects the growth, reproduction, and physiology of fish, which is threatening the sustainable development of the aquaculture sector. Recently, several techniques, such as adsorption, physio-biochemical, molecular, and phytoremediation mechanisms have been successfully applied to reduce the toxicants in the environment. Microorganisms, especially several bacterial species, play a key role in this bioremediation process. In this context, the present review summarizes the bioaccumulation of different heavy metals into fishes, their toxic effects, and possible bioremediation techniques to protect the fishes from heavy metal contamination. Additionally, this paper discusses existing strategies to bioremediate heavy metals from aquatic ecosystems and the scope of genetic and molecular approaches for the effective bioremediation of heavy metals.
... The microbial cell wall, which is mainly composed of polysaccharides, lipids, and proteins, provides many functional groups capable of binding heavy metals, including carboxylate, hydroxyl, amino, and phosphate groups (Scott & Karanjkar, 1992). Among the various reactive compounds associated with bacterial cell walls, extracellular polymeric substances (EPS) are well known to have significant effects on acid-base properties and heavy metal absorption (Guiné et al., 2006). The enrichment of heavy metals is a process in which microorganisms absorb heavy metals from the surrounding environment and deposit them in the cell (Li & Tao, 2015). ...
Owing to the ecological applicability, phytoremediation has attracted extensive attention in the remediation of heavy metals–contaminated soil, but the slow plant growth and low remediation efficiency limit its application. Recently, the developed plant-associated microbes has opened up promising areas of research in the field of phytoremediation technology. Various plant growth–promoting rhizobacterias (PGPR) are suggested to be involved in the phytoremediation of heavy metals–contaminated soils, thereby significantly enhancing the removal efficiency of heavy metals. Currently, the published reviews focus on the resistance mechanism of plants and microorganisms to heavy metals, but the function and regulatory machinery of PGPR on phytoremediation have been overlooked. This paper will give a critical review on the processes of PGPR in phytoremediation, including both direct and indirect mechanisms such as (i) the secretion of siderophores, organic acids, biosurfactants, and redox processes and (ii) stimulating plant growth or enhancing their resistance via N fixation, P solubilization, and phytohormone and aminocyclopropane-1-carboxylic acid deaminase synthesis. Moreover, the development of PGPR in phytoremediation is prospected. This work would help readers and researchers better understand the principle and application of PGPR in promoting phytoremediation heavy metals–contaminated soil.
... The extended X-ray absorption fine-structure (EXAFS) spectroscopy and equilibrium titration studies performed by Guiné et al. [89] indicated that zinc(II) is primarily complexed with phosphoester, carboxyl, and sulfhydryl ligands in P. putida ATCC 12633 biomass and, more importantly, EPSs play the dominant role in zinc retention compared with other cell components (e.g., periplasmic space, outer membrane) with reactive site densities of 16 zinc·nm −2 . Additionally, Lin et al. [90] noted that the K-edge X-ray absorption nearedge structure (XANES) analysis showed that, besides the cell walls' and cell membranes' phospholipids and intracellular thiol-rich proteins, the acidic polysaccharide alginate in EPS played a crucial role in copper(II) binding in P. putida CZ1. ...
Pseudomonas biofilms have been studied intensively for several decades and research outcomes have been successfully implemented in various medical and agricultural applications. Research on biofilm synthesis and composition has also overlapped with the objectives of environmental sciences, since biofilm components show exceptional physicochemical properties applicable to remediation techniques. Especially, exopolysaccharides (ExPs) have been at the center of scientific interest, indicating their potential in solving the environmental issues of heavy metal land and water contamination via sorptive interactions and flocculation. Since exposure to heavy metal via contaminated water or soil poses an imminent risk to the environment and human health, ExPs provide an interesting and viable solution to this issue, alongside other effective and green remedial techniques (e.g., phytostabilization, implementation of biosolids, and biosorption using agricultural wastes) aiming to restore contaminated sites to their natural, pollution-free state, or to ameliorate the negative impact of heavy metals on the environment. Thus, we discuss the plausible role and performance of Pseudomonas ExPs in remediation techniques, aiming to provide the relevant available and comprehensive information on ExPs’ biosynthesis and their usage in heavy metal remediation or other environmental applications, such as wastewater treatment via bioflocculation and soil remediation.
... Data normalization and linear combination fits were achieved using Athena Demeter® software (Athena, Demeter, (Ravel and Newville, 2005)). The library of Zn reference compounds has been described previously (Guiné et al., 2006;Sarret et al., 2006). Three samples of Zn sorbed on amorphous SiO2 (Zn-SiO2am) were prepared as follows: a suspension of Zn aerosil 200 (Degussa) was pre-equilibrated at the desired pH (6.0 or 7.2) by addition of NaOH 0.5M, resulting in an ionic strength of 0.5 mM. ...
Phytoliths are microscopic structures made of amorphous opal (opal-A), an amorphous hydrated silica, dispersed within plant tissues and persisting after the decay of the plant. Silicon is known to alleviate metal toxicity in plants, but the role of phytoliths in metal sequestration and detoxification is unclear. Dry ashing, the most common protocol for phytolith extraction, was previously shown to lead to sequestration of metals by the phytoliths; however, the mechanisms of this process remained elusive. The purpose of this study was to evaluate whether the association between metals and phytoliths results from dry ashing or pre-exists in plant tissues. Thus, we compared phytoliths extracted by dry ashing at 700 °C and plant leaves before and after dry ashing. A combination of ICP-MS, XRD, SEM-EDX and Zn-K-edge EXAFS spectroscopy was used to assess elemental concentrations, morphology and crystallography of silica, and chemical status of Zn. Results demonstrated a phase transition from amorphous opal (opal-A) to opal-CT and α-cristobalite, and the sequestration of metal in phytoliths during dry ashing. For Zn, Mn and Pb, a linear relationship was found between the concentration in phytoliths and in leaves. In the phytoliths, Zn was sequestered in silica in tetrahedral configuration. We hypothesize that this association results form a solid-state reaction during ashing, involving a redistribution of Zn from the organic material to the silica, possibly promoted by the release of structural water from amorphous opal throughout the heating procedure. This study improves our understanding of the impact of high temperature treatments on plant biomass and phytoliths. It suggests that Zn toxicity alleviation in plants by silicon does not rely on its sequestration by phytoliths. In natural settings, wild fire events and biomass burning may lead to metal sequestration in low-soluble form, which should be considered in modeling of biogeochemical cycles and in paleoenvironmental studies.
... Bacillus subtilis exhibits high tolerance and adsorption capacity for metals like Cd, Cr, Mn, and Pb, thereby representing a potential means for the detoxification and elimination of metal ions. was bound to phosphate groups of Pseudomonas putida while only 20% of Zn(II) was bound to carboxyl groups (Toner et al., 2005;Guiné et al., 2006). Additional studies have confirmed that sulfhydryl groups play important roles in the adsorption of HMs on cell walls. ...
Heavy metal (HM) pollution of soils is a globally important ecological and environmental problem. Previous studies have focused on i) tracking pollution sources in HM-contaminated soils, ii) exploring the adsorption capacity and distribution of HMs, and iii) assessing phyto-uptake of HMs and their ecotoxicity. However, few reviews have systematically summarized HM pollution in soil-plant systems over the past decade. Understanding the mechanisms of interaction between HMs and solid soil components is consequently key to effectively controlling and remediating HM pollution. However, the compositions of solid soil phases are diverse, their structures are complex, and their spatial arrangements are heterogeneous, all leading to the formation of soil micro-domains that exhibit different particle sizes and surface properties. The various soil components and their interactions ultimately control the speciation, transformation, and bioavailability of HMs in soils. Over the past few decades, the extensive application of advanced instrumental techniques and methods has greatly expanded our understanding of the behavior of HMs in organic mineral assemblages. In this review, studies investigating the immobilization of HMs by minerals, organic compounds, microorganisms, and their associated complexes are summarized, with a particular emphasis on the interfacial adsorption and immobilization of HMs. In addition, methods for analyzing the speciation and distribution of HMs in aggregates of natural soils with different particle sizes are also discussed. Moreover, we also review the methods for speciating HMs at mineral-organic micro-scale interfaces. Lastly, developmental prospects for HM research at inorganic-organic interfaces are outlined. In future research, the most advanced methods should be used to characterize the interfaces and in situ characteristics of metals and metal complexes. In particular, the roles and contributions of microorganisms in the immobilization of HMs at complex mineral-organic interfaces require significant further investigation.
... Under high metal loading conditions (metal:bacteria ratios >10 mmol of aqueous metal/gram of wet biomass), carboxyl and phosphoryl groups are the most important metal bindings sites on bacterial cell surfaces, largely because they are present on the surfaces at higher concentrations than other binding site types (Beveridge and Murray 1980;Jiang et al. 2004;Ngwenya et al. 2003). However, recent studies have demonstrated that sulfhydryl sites, a type of low abundance, high affinity site that is present on a wide range of bacterial cell surfaces, become the dominant binding sites for many chalcophile metals under low metal loading conditions (Guine et al. 2006;Mishra et al. 2010;Pokrovsky et al. 2012;Yu and Fein 2015). Here, chalcophile metals are defined as metals such as Hg, Cd, Zn, Pb and Au that have stronger interactions with sulfur than with oxygen, and most of these metals are of high environmental concern due to their high toxicity and occurrence as industrial and mining contaminants. ...
Understanding the controls on bacterial surface sulfhydryl site concentrations is crucial for modeling the effects of bacterial cells on the fate and transport of chalcophile metals in the environment. In this study, we investigate the effects of changing the concentrations of MgSO4, NaCl and NaNO3 in a growth medium on the concentration of cell surface sulfhydryl sites on the Gram-positive bacterial species Bacillus subtilis, as measured using a potentiometric titration approach. Our results show that the concentration of MgSO4 in a M9 minimal medium exerts a strong influence on bacterial surface sulfhydryl site concentrations under low MgSO4 concentrations but that this effect plateaus with increasing MgSO4 concentrations, indicating that a minimum amount of a sulfur source is required for bacteria to produce cell surface sulfhydryl sites. Although the sulfhydryl site concentration was below the detection limit on biomass samples that were grown in a M9 minimal medium containing 0.1 mM MgSO4, increasing the concentration of either NaCl or NaNO3 in the medium yielded biomass samples with measurable sulfhydryl site concentrations on the cell surface. In contrast, adding NaClO4 to the M9 medium did not increase cell surface sulfhydryl site concentrations. The NaCl and NaNO3 effects likely arise because increasing the concentration of NaCl or NaNO3 in a M9 minimal medium can promote the production of EPS by bacteria, and because the surface sulfhydryl sites of B. subtilis are located mostly on its EPS molecules. The results of this study suggest that bacterial nutrients and water chemistry composition are key controls on the abundance of bacterial surface sulfhydryl sites.
... The sites with pKa = 5.9 can be assigned to carboxyl groups. The pKa values of carboxylic groups are between 2 and 6 ( Guiné et al., 2006;Dittrich and Sibler, 2005). The pKa value of 5.9 meant that the acidic carboxylic groups on the bacterial surfaces were linked to the short-chained aliphatic chains rather than the aromatic groups (Naja et al., 2005;Fein et al., 1997). ...
Although ferric iron in extracellular polymeric substances (EPS) was believed to be pivotal in bioleaching, the real existing form of ferric iron in EPS has remained poorly understood. In this study, whole cells of Acidithiobacillus ferrooxidans were used to study the composition and properties of EPS. The components sugars, proteins and uronic acids could be extracted from cells rich in EPS. Four distinct surface functional groups were characterized on the bacterial surfaces by the fitting of titration data. Subsequently, these functional groups were confirmed as carboxyl groups, phosphoryl groups, thiol groups, and amine groups by combining FTIR and XPS. However, with the help of modeling results and FTIR, these functional groups failed to dissociate protons in a strong acidic environment. The protonated functional groups could unlikely complex ferric iron according to the site-specific surface complexation theory. Besides, the isolated EPS could not sharply reduce the concentration of free ferric ions, and the ferric iron could be removed by washing the cell surfaces with HClO4. These results indicate that there is no strong chemical interaction between bacteria and ferric iron. This study suggests a weak interaction of ferric iron with the EPS of A. ferrooxidans, and gives some deeper insight into the microenvironment of EPS.
... The role of sulfhydryl groups in Pb stabilization has been largely ignored in previous studies at high Pb loading (Chen et al., 2020;Qu et al., 2018). Similarly to the present work, EXAFS-based analysis has revealed preferential adsorption of Cd, Zn and Au onto sulfhydryl, when applied at low concentrations, in gram-negative bacteria (Mishra et al., 2010;Guiné et al., 2006;Song et al., 2012). Therefore, the binding of chalcophile elements to gram-negative bacteria is concentration dependent, with S-containing groups being the most occupied functional groups at low metal concentrations. ...
Bacteria and their secreted extracellular polymeric substances (EPS) are widely distributed in ecosystems and have high capacity for heavy metal immobilization. The knowledge about the molecular-level interactions with heavy metal ions is essential for predicting the behavior of heavy metals in natural and engineering systems. This comprehensive study using potentiometric titration, Fourier-transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) was able to reveal the functional diversity and adsorption mechanisms for Pb onto bacteira and the EPS in greater detail than ever before. We identified mono-carboxylic, multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites and found the partitioning of Pb to these functional groups varied between gram-negative and gram-positive bacterial strains, the soluble and cell-bound EPS and Pb concentrations. The sulfhydryl and phosphodiester groups preferentially complexed with Pb in P. putida cells, while multifunctional carboxylic groups promoted Pb adsorption in B. subtilis cells and the protein fractions in EPS. Though the functional site diversity, the adsorption of Pb to organic ligands occurred spontaneously through a universal entropy increase and inner-sphere complexation mechanism. The functional group scale knowledge have implications for the modeling of heavy metal behavior in the environment and application of these biological resources.
... Microorganisms may biosorb toxic metals on binding regions throughout the cellular organization without the use of energy. Exopolymeric molecules seem to be of special significance among the many reactive chemical compounds linked with microbial cell walls and they are documented to possess considerable impacts on acid-base characteristics including metal adsorption (Guin e et al. 2006). Complexation, coordination, chelation, ion exchange, and microprecipitation are some of the biosorption processes that can be used (Pokethitiyook and Poolpak 2016). ...
Heavy metals contaminations in soil adversely affect the growth and survibality of the plants. Alternatively, plants have evolved complex physiological processes to withstand such environmental cues. Myraids of plant varieties with improved tolerance to metal toxicity has been developed through molecular breeding and transgenic approaches. However, such methods are laborious, expensive and not 100% effective. Recent evidences indicate that several microbes can tolerate metal toxicity and can acclimatize to adverse environmental conditions. The association of plants and such metal-tolerant microbes could be one of the promising strategies to enhance plant performance under metal toxicity. In this review, we focus on the association between plant and microbes in alleviating metal toxicity. We have also presented the different physiological processes
of achieving metal toxicity in plants. Furthermore, different strategies to improve plant resilience through microbial applications have been discussed.
... Also genes coding for glucans were found, such as 1,4-alpha-glucan branching enzyme (GlgB) [100], the 1,4-beta-D-glucan glucohydrolase (GghA) [101], 4-alpha-glucanotransferase (MalQ) [102], alpha-1,4-glucan:maltose-1-phosphate maltosyltransferase (GlgE) [103,104], beta-glucanase (BglA) [105,106], glucan synthase (NdvB) [107] and the Endoglucanase (Egl) [108]. Osmoregulated periplasmic glucans are part of EPS and have been found to play a role in bacteria that respond to harsh conditions such as osmotic [109] and heavy-metal stresses [110,111]. The role of EPS in photosynthetic environments rich in metal has been demonstrated [17, [112][113][114] as the negative charge assumed in high pH, i.e., during high photosynthetic regimes, might sequestrate toxic, positively charged metal ions. ...
The Swiss Alpine environments are poorly described from a microbiological perspective. Near the Greina plateau in the Camadra valley in Ticino (southern Swiss Alps), a green-turquoise-coloured water spring streams off the mountain cliffs. Geochemical profiling revealed naturally elevated concentrations of heavy metals such as copper, lithium, zinc and cadmium, which are highly unusual for the geomorphology of the region. Of particular interest, was the presence of a thick biofilm, that was revealed by microscopic analysis to be mainly composed of Cyanobacteria. A metagenome was further assembled to detail the genes found in this environment. A multitude of genes for resistance/tolerance to high heavy metal concentrations were indeed found, such as, various transport systems, and genes involved in the synthesis of extracellular polymeric substances (EPS). EPS have been evoked as a central component in photosynthetic environments rich in heavy metals, for their ability to drive the sequestration of toxic, positively-charged metal ions under high regimes of cyanobacteria-driven photosynthesis. The results of this study provide a geochemical and microbiological description of this unusual environment in the southern Swiss Alps, the role of cyanobacterial photosynthesis in metal resistance, and the potential role of such microbial community in bioremediation of metal-contaminated environments.
... The binding of metals to these cellular structures is metabolic energy independent. The various reactive species on bacterial cell wall show significant effects on the acid-base properties and metal adsorption (Guiné et al., 2006). Extracellular polymeric substances (EPS) can combine with complex heavy metals via various mechanisms, including proton exchange and micro-precipitation of metals (Comte et al., 2008;Fang et al., 2010). ...
About the Book This book describes the uniqueness of compost at various geographic regions. The importance of process control parameters are described details which are very much meaningful for the preparation of quality compost. Important addition is the technology incorporation to enrich the compost through designing of composting method, selecting appropriate substrate, their proportionate blending and fortification of micronutrients for the site specific application. Extensive role of microbial activities and different types of composting preparation procedures summarized in details. This book uniquely describes how Indian cities become near zero waste following India's six new waste management rules of 2016. This book provides the updated concepts and technologies in composting manure preparation, and basic knowledge on composting technology and their large-scale management. It also describes a variety of composting types and their beneficial role for both farmers and the ecosystem. The book has been divided into fourteen chapters that balance the composting enrichment process with value addition, top to bottom composting process from raw materials to municipal waste, and their uses in different parts of India. Role of microbial diversity in multistep composting process has been well described. One chapter is dedicated to recent updates on nanofertilizers and their future concerns. This book is highly relevant to the students of Environmental Studies, Microbiology, Biotechnology, Botany, Zoology, Plant Protection, Agriculture and Agronomy. Salient Features improvement of soil quality through continuous application of nutrient enriched (phospho-sulfo-nitro) organic compost along with normal quantities of mineral additives. process control parameters for the preparation of quality compost. technology to enrich the compost through designing of composting method, selecting appropriate substrate, their proportionate blending and fortification of micronutrients for the site specific application. Textbook
... X-ray absorption fine structure (XAFS) spectroscopy yields information on the local coordination environment of a metal adsorbed to a mineral or microbial surface. XAFS of fungal cell walls (Sarret et al., 1998), Grampositive bacteria (Kelly et al., 2002;Boyanov et al., 2003), and Gramnegative bacteria (Toner et al., 2005;Guiné et al., 2006) indicate that phosphoryl, carboxyl, and sulfhydryl functional groups are responsible for the metal complexation on each of these organisms. To our knowledge, few XAFS studies have investigated the molecular mechanisms of heavy metal adsorption by EPS. ...
Biosorption mechanisms of Cu(II) by extracellular polymeric substances (EPS) from Bacillus subtilis were investigated using a combination of batch experiments, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, isothermal titration calorimetry (ITC), and X-ray absorption fine structure (XAFS) spectros-copy. A three discrete site non-electrostatic model fit the potentiometric titration data best, with the pK a values of 4.12 ± 0.12, 6.60 ± 0.06, and 9.09 ± 0.03, and site concentrations of 4.81 ± 0.62 × 10 −3 , 2.16 ± 0.14 × 10 −3 , and 2.87 ± 0.21 × 10 −3 mol per gram dry mass of EPS, respectively. The ATR-FTIR results confirmed the presence of the functional groups with above pK a values within the EPS molecules, and indicated that Cu(II) binding onto the EPS involves either phosphoryl or carboxyl sites, or both. The calculated enthalpies and entropies of Cu(II) adsorption onto EPS suggest that Cu(II) binds with anionic oxygen-bearing ligands and forms inner-sphere complexes with the EPS functional groups. The XAFS results were consistent with inner-sphere binding of Cu(II) by carboxyl sites with 2.03 C atoms at distance of 2.96 Å in the second shell, which further suggests that the carboxyl groups are the dominant sites for Cu(II) adsorption by EPS at pH 5.0, and that a five-membered chelate ring structure is the most likely binding environment for Cu(II) bound to EPS. The molecular binding mechanisms obtained in this study will add fundamental knowledge of understanding the fate of heavy metals in natural environments.
... The order of buffering capacity for pure mineral systems was goethite > montmorillonite > kaolinite, while that for bacteria was B. thuringiensis > P. putida. Surface functional groups are the basic units of surface complexation reactions on bacteria or minerals [25,26]. The deprotonation of a functional group can be represented by the following generic reaction [27]: ...
In order to have a better understanding of the interactions of heavy metals with bacteria and minerals
in soil and associated environments, isothermal titration calorimetry (ITC), potentiometric titration
and equilibrium sorption experiments were conducted to investigate the adsorption behavior of Cu(II)
by Bacillus thuringiensis, Pseudomonas putida and their composites with minerals. The interaction of
montmorillonite with bacteria increased the reactive sites and resulted in greater adsorption for
Cu(II) on their composites, while decreased adsorption sites and capacities for Cu(II) were observed
on goethite–bacteria composites. A gram-positive bacterium B. thuringiensis played a more important
role than a gram-negative bacterium P. putida in determining the properties of the bacteria–minerals
interfaces. The enthalpy changes (�Hads) from endothermic (6.14 kJ mol−1) to slightly exothermic
(−0.78 kJ mol−1) suggested that Cu(II) is complexed with the anionic oxygen ligands on the surface
of bacteria–mineral composites. Large entropies (32.96–58.89 J mol−1 K−1) of Cu(II) adsorption onto
bacteria–mineral composites demonstrated the formation of inner-sphere complexes in the presence
of bacteria. The thermodynamic data implied that Cu(II) mainly bound to the carboxyl and phosphoryl
groups as inner-sphere complexes on bacteria and mineral–bacteria composites.
... A variety of surface functional groups on bacterial cell walls such as carboxyls, phosphomonoesters, phosphodiesters, amines and hydroxyls have been suggested to be directly responsible for the reactivity of bacterial cells [4][5][6]. Among them carboxyl and phosphoryl groups are considered to be particularly important in metal complexation based on wet chemistry and modeling studies [7][8][9][10]. ...
In this study, Fourier transform infrared spectroscopy, potentiometric titration, along with sorption
experiments using chemically modified bacteria were conducted to compare the behavior of Grampositive
Bacillus thuringiensis and Gram-negative Escherichia coli as sorbents for Cu2+ and Cd2+ ions.
The IR spectra showed that there were obvious changes connected with the–COOH groups for Cu(II)-
and Cd(II)-loaded B. thuringiensis. A three site non-electrostatic model provides an excellent fit to the
titration curves of both E. coli and B. thuringiensis with the first corresponding pKa values of 4.16±0.18
and 3.30±0.24, respectively, implying that B. thuringiensis contains more carboxyl groups than E. coli.
Chemical modification and metal sorption experiments further confirmed that carboxyl groups may
play a more important role in the binding Cd(II) and Cu(II) for B. thuringiensis than for E. coli, which
could be attributed to the higher concentration of carboxyl sites of B. thuringiensis than E. coli. These
results show that the main chemical functional group responsible for the binding of metal ions on B.
thuringiensis and E. coli is obviously different because of the different composition and structure of bacterial
cell walls. The concentrations of the chemical functional groups on bacterial cell walls are regarded
to govern their role in the binding of metal ions and affect the affinity between the bacterial cells and
metal ions.
... According to the conformation of EPS-PN, stable non-fluorescence complexes could be formed between EPS-PN and Cd 2þ , resulting in decreased intensities of fluorescence peaks A and B. In fact, this was consistent with what reported in the literature (Sheng et al., 2013a(Sheng et al., , 2013b. It had been proposed that heavy metal ions could primarily bind to the functional groups of EPS-PN through chemical complexation , such as phosphate, carboxyl, amine and hydroxyl groups in EPS-PN (Guin e et al., 2006). In this study, the FTIR spectra of EPS were used to demonstrate the binding of Cd 2þ to EPS (Fig. 4). ...
So far, the microalgal-bacterial granular sludge process has attracted growing interest as an emerging wastewater treatment technology. Cadmium ion (Cd²⁺) commonly found in wastewater is toxic to microorganisms, thus its effect on microalgal-bacterial granules was investigated in this study. Results showed that Cd²⁺ at the concentration above 1 mg/L could compromise the performances of microalgal-bacterial granules. The removal efficiency of chemical oxygen demand decreased from about 70% in the control to 42.2% and 25.0% after 30-day operation at the respective Cd²⁺ concentrations of 5 and 10 mg/L, while the ammonia-nitrogen removal also declined from 70.4% to 30.5% with the increase of the Cd²⁺ concentration from 1 to 10 mg/L, indicating that nitrifying bacteria were susceptive to the presence of Cd²⁺. It was further revealed that Cd²⁺ could stimulate the production of extracellular polymeric substances, e.g. 190.19 ± 7.04 mg/g VSS in the presence of 10 mg/L of Cd²⁺ versus 100.26 ± 3.82 mg/g VSS in the control after 10-day operation. More importantly, about 84.1%–94.8% of Cd²⁺ was found to bind to the extracellular proteins in microalgal-bacterial granules at the Cd²⁺ concentrations studied. In addition, Chlorococcum and Cyanobacteria in microalgal-bacteria granules were withered in the presence of 10 mg/L of Cd²⁺, suggesting uncoupled symbiosis between microalgae and bacteria induced by Cd²⁺. Consequently, this study showed that Cd²⁺ could negatively impact on the microbial structures and metabolisms of microalgal-bacterial granular sludge, leading to a compromised process performance in terms of organic and nitrogen removal.
... Activated carbon has also been used in wastewater treatment. There are various reactive compounds present on the surface of microorganisms, called extracellular polymeric substances (EPS), which are reported to have significant effects on acid-base properties and metal adsorption (Guiné et al., 2006). EPS can form complexes with heavy metals using various mechanisms like proton exchange and microprecipitation of metals (Comte, Guibaud, & Baudu, 2008;Fang et al., 2010). ...
Unchecked release of toxic heavy metals in industrial effluents and its environmental and public health implications have opened up a huge opportunity for environment biotechnological applications. Pollutants may be assimilated by the organism, disintegrated into less toxic compounds, or concentrated by adsorption onto the surface of dead biomass. Microalgae, rightly named as a “wonder organism,” are capable of accomplishing bioremediation efficiently by two mechanisms, namely, bioassimilation and biosorption. They have the capability to grow in polluted water as “algal blooms” and assimilate various pollutants. The algal biomass, after harvesting and lipid/protein extraction, could be used as an efficient biosorbent. Careful consideration of parameters such as growth conditions, cellular structure, pretreatment of biomass, etc. can result in development of a low-cost microalgae-based biomass with high bioremediation potential to neutralize and adsorb heavy metal ions. Hence, this chapter discusses the various avenues for bioremediation of toxic heavy metals using the biomass of microalgae.
... The development of predictive models for adsorption ( Figure 1) is a practical demonstration of this approach, in which bench-scale macroscopic experiments identify model limitations and synchrotron spectroscopy guides model refinement [30][31][32]. This approach has been applied to studying adsorption onto minerals, bacteria, and organic matter, all components in water treatment systems [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Recent advances in the application of synchrotron spectroscopy to emerging water treatment technologies, such as membrane processes, are taking a similar approach. ...
... the extracellular polymeric substances, are of precise importance and are widely recognized to have a massive effect on acidÀbase properties and arsenic adsorption (Sikkema et al., 1995). Studies on the arsenic binding behavior of extracellular polymeric substances (EPS) discovered a brilliant ability to form complexes through various mechanisms, which consist of proton exchange and microprecipitation of arsenic (Guiné et al., 2006;Comte et al., 2008). Recent studies have characterized and quantified the proton and adsorbed arsenic on bacterial cells and EPS free cells to determine the relative significance of EPS molecules in arsenic elimination (Fang et al., 2011). ...
... The bacterial surfaces of B. subtilis and P. putida contain both regions which promote hydrophobic binding and proton-active binding sites which lead to a negativelycharged surface at the pH values of these experiments. The proton-active binding sites include carboxyl, hydroxyl, amine (Beveridge and Murray, 1980), and sulfhydryl groups (Guiné et al., 2006;Yu et al., 2014). Although the surfaces of both bacteria species are negativelycharged under the pH conditions of the experiments leading to electrostatic repulsion of negatively-charged PFOS and PFOA as a whole, sites which are positively charged at lower pH values, e.g. ...
... To determine mechanisms of enhanced REE biosorption on engineered cell surfaces, REE complexation by wild type (e.g., nonengineered) cell surfaces must first be understood. Bacteria cell walls are complex and contain multiple types of functional groups, including carboxyl, hydroxyl, phosphoryl (Fein et al., 1997), sulfhydryl (Yu and Fein, 2015;Mishra et al., 2017), and amine groups (Borrok et al., 2005;Guin� e et al., 2006). Rare earth element biosorption onto bacterial surfaces has been shown to be predominantly controlled by carboxyl and phosphoryl functional groups (Texier et al., 2000;Markai et al., 2003;Ngwenya et al., 2009Ngwenya et al., , 2010. ...
Lanthanide binding tags (LBTs) have been engineered onto the cell surface of E. coli to enhance biosorption and recovery of rare earth elements (REEs). The protonation behavior of the bacterial surfaces before and after LBT-display was compared by modeling acid-base titration data. A multiple discrete site, constant capacitance surface complexation model was constructed to examine rare earth (Tb) binding to cell surface functional groups, comparing wild type and LBT-engineered surfaces. Our acid-base titrations show similar pKa values between the two strains, suggesting induction of LBTs does not significantly alter cell surface protonation behavior. Tb sorption onto the wild type cell surface can be captured by a one-site carboxyl model. The LBT strain exhibited a higher metal loading that can be explained by the increase of sorption sites in the form of lanthanide binding tags. Furthermore, carboxyl site concentrations between wild type and LBT-induced cells were statistically indistinguishable. We thus attribute the engineered strains’ increase in Tb adsorption capacity and affinity to the addition of lanthanide binding tags to the cell surface. The Tb stability constant with the LBT site is two orders of magnitude higher than that with the carboxyl functional group. As a result, at low metal loading <10 μM, the Tb binding to the cell surface of the LBT-strain is controlled by the presence of high-affinity, but lower capacity, LBT sites. At higher metal loadings >10 μM, a more abundant but low affinity functional group becomes the main source of adsorption that results in an overall higher sorption capacity. This work demonstrates how surface complexation modeling can be implemented for bacterial surfaces engineered with a known protein tag to optimize REE recovery from fluids with variable pH and metal loadings.
... Plus précisément, les éléments traces métalliques se complexent avec les groupements fonctionnels des molécules organiques (groupes aminés, groupes phosphatés, acides carboxyliques) (Aulin et al. 1997 ;C. Durand 2003 ;Muris 2004 ;Causse 2009 ;Guiné et al. 2006 ;Schulin, Geiger et Furrer 1995). De plus, la matière organique, dont le pouvoir d'adsorption cationique est élevé (entre 2000 et 5000 meq/kg (Musy et Soutter 1991)), peut retenir les ETM sous forme échangeable et mobilisable (Larmet 2007b ;Roger et al. 1998). ...
Les sédiments urbains et résidus minier sont deux sources de pollution potentielle pour l’environnement et plus particulièrement les eaux de surfaces ou les eaux souterraines. L’altération chimique de ces interfaces solides par contact avec une source d’acidité ou d’alcalinité via l’air ou l’eau, est susceptible de se traduire par une dissolution des phases minérales et organiques et d’induire une mobilisation des éléments majeurs et traces métalliques. Ces mécanismes sont encore mal décrits et modélisés pour ce type de matrices très complexes. Cette thèse étudie donc le potentiel de mobilisation des éléments majeurs et traces métalliques de diverses interfaces carbonaté ou non carbonaté (pour l’étude du drainage minier acide et neutre contaminé). En supplément, des interfaces minérales pures ont été utilisées pour simuler en laboratoire des assemblages de phases et identifier les mécanismes croisés impliqués dans le drainage minier acide et neutre contaminé. Toutes ces matrices ont été soumises à des tests de capacité de neutralisation acido-basique (mise en contact avec une source de protons ou d’alcalinité), avec le suivi du pH (pouvoir tampon), de la conductivité et de la mobilisation élémentaire (majeurs et éléments traces métalliques). Les données expérimentales ont été modélisées avec le logiciel de spéciation géochimique PHREEQC. La combinaison des volets d’expérimentation et de modélisation, qui a très rarement été développé sur des interfaces solides aussi complexes, a permis l’identification (i) des réactions de dissolution des phases constitutives des interfaces polluées avec les réactions de sorption impliquées dans la mobilisation de leurs éléments majeurs et traces métalliques, (ii) de la spéciation des éléments majeurs et traces métalliques dans ces interfaces et dans les solutions en équilibre avec les phases solides. Ce travail de thèse permet donc d’aboutir à une méthodologie robuste, précise et réplicable permettant une caractérisation fine de la spéciation en phase liquide et solide des polluants métalliques dans les interfaces contaminées. Cette méthodologie constitue une base cruciale pour comprendre et prédire l’évolution des matières solides contaminées (sédiments urbains et déchets miniers) en fonction des différents modes de gestion : dépollution, valorisation et recyclage.
... It is known that microorganisms play an important role in heavy metal immobilization processes (Cheng et al., 2010) either at extracellular (biosorption) and/or intra-cellular (bioaccumulation) levels (Guibaud et al., 2005;Guin e et al., 2006;Kothe et al., 2010;Puyen et al., 2012b;Esteve et al., 2013;Burgos et al., 2013;Guti errez-Corona et al., 2016). On the other hand, Vel asquez and Dussan (2009) demonstrated the relation between external capture and passive process (live or dead cells) and internal bioaccumulation and active process (live cells). ...
Ochrobactrum anthropi DE2010 is a microorganism isolated from Ebro Delta microbial mats and able to resist high doses of chromium(III) due to its capacity to tolerate, absorb and accumulate this metal. The effect of this pollutant on O. anthropi DE2010 has been studied assessing changes in viability and biomass, sorption yields and removal efficiencies. Furthermore, and for the first time, its capacity for immobilizing Cr(III) from culture media was tested by a combination of High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) imaging coupled to Energy Dispersive X-ray spectroscopy (EDX). The results showed that O. anthropi DE2010 was grown optimally at 0-2 mM Cr(III). On the other hand, from 2 to 10 mM Cr(III) microbial plate counts, growth rates, cell viability, and biomass decreased while extracellular polymeric substances (EPS) production increases. Furthermore, this bacterium had a great ability to remove Cr(III) at 10 mM (q = 950.00 mg g-1) immobilizing it mostly in bright polyphosphate inclusions and secondarily on the cellular surface at the EPS level. Based on these results, O. anthropi DE2010 could be considered as a potential agent for bioremediation in Cr(III) contaminated environments.
... Heavy metals form interactions with the binding sites present in the cellular structure of bacteria through biosorption method. Extracellular polymeric substances (EPS) of bacterial cell walls have significant properties for metal adsorption and EPS revealed a great ability to form complex through specific mechanisms for the precipitatation of metals (Guine et al., 2006;Comte et al., 2008;Fang et al., 2010). Fang et al. (2011) characterized and quantified proton and adsorbed on bacterial cells and studied the importance of EPS molecules to remove the toxic metal. ...
An increase in industrialization and various kind of human activities added a huge amount of toxic heavy metals in the soil. As a result, toxic heavy metals in the environment may be adversely affects human being and aquatic ecosystem. Thus, it is very essential to understand mechanism of bioremediation through eco-friendly agent i.e. bacteria. Accumulation of high metal concentrations in soil above threshold limit causes lethal to bacterial communities in the environment. Few bacteria develop resistance mechanism to tolerate these toxic heavy metals and contain various methods to respond the metal stress. The present review emphasizes to understand the mechanism of bacterial resistance against toxic metals. Moreover, mechanism of bioaugmentation, biosorption, and bioaccumulation methods also described clearly.
To explore the role of biofilm formation on the corrosion of marine concrete structures, we investigated the attachment of biofilm on mortar surfaces in simulated seawater and the influence of biofilm on the microstructure of mortar surfaces. The results show that the evolution of biofilm on mortar surfaces in simulated seawater is closely related to the corrosion suffered by the mortar, and the process of biofilm attachment and shedding is continuous and cyclical. It is found that the specimens in the absence of biofilm attachment are more severely eroded internally by the corrosive medium in simulated seawater than those in the presence of biofilm attachment. For the specimens without biofilm attachment, after 60 days, gypsum forms, and after 120 days, the number of pores in the mortar is reduced. In contrast, for the specimens in the presence of biofilm attachment, gypsum could only be detected after 90 days, and fewer pores are filled. Therefore, the formation of biofilm could delay the invasion of the corrosive medium into the interior of mortar during the evolution of biofilm on mortar surfaces, mitigating the corrosion of mortars in seawater.
Plastics and synthetic polymers are mainly produced from petrol chemical elements, which do not decompose and are a major cause of environmental pollution. This has led to an increased demand for natural polymers or biopolymers. Poly-3-hydroxybutyrate (PHB), a Biological polymer is a good alternative to plastic, is environmental friendly, and does not cause pollution. Exopolysaccharides or Extracellular Polymeric Substances (EPS) are produced by microorganisms as soluble or insoluble polymers and have diverse applications in various industries. This article gives an insight into PHB and EPS and their production from marine bacteria.
Increased industrial and agricultural activity has led to the contamination of the earth's soil and groundwater resources with hazardous chemicals. The presence of heavy metals, dyes, fluorides, dissolved solids, and many other pollutants used in industry and agriculture are responsible for hazardous levels of water pollution. The removal of these pollutants in water resources is challenging. Bioremediation is a new technique that employs living organisms, usually bacteria and fungi, to remove pollutants from soil and water, preferably in situ. This approach is more cost-effective than traditional techniques, such as incineration of soils and carbon filtration of water. It requires understanding how organisms consume and transform polluting chemicals, survive in polluted environments, and how they should be employed in the field. Bioremediation for Environmental Pollutants discusses the latest research in green chemistry and practices and principles involved in quality improvement of water by remediation. It covers different aspects of environmental problems and their remedies with up-to-date developments in the field of bioremediation of industrial/environmental pollutants. Volume 1 focuses on the bioremediation of heavy metals, pesticides, textile dyes removal, petroleum hydrocarbon, microplastics and plastics.
Microorganisms can oxidize Mn(II) to biogenic Mn oxides (BioMnOx), through enzyme-mediated processes and non-enzyme-mediated processes, which are generally considered as the source and sink of heavy metals due to highly reactive to sequestrate and oxidize heavy metals. Hence, the summary of interactions between Mn(II) oxidizing microorganisms (MnOM) and heavy metals is benefit for further work on microbial-mediated self-purification of water bodies. This review comprehensively summarizes the interactions between MnOM and heavy metals. The processes of BioMnOx production by MnOM has been firstly discussed. Moreover, the interactions between BioMnOx and various heavy metals are critically discussed. On the one hand, modes for heavy metals adsorbed on BioMnOx are summarized, such as electrostatic attraction, oxidative precipitation, ion exchange, surface complexation, and autocatalytic oxidation. On the other hand, adsorption and oxidation of representative heavy metals based on BioMnOx/Mn(II) are also discussed. Thirdly, the interactions between MnOM and heavy metals are also focused on. Finally, several perspectives which will contribute to future research are proposed. This review provides insight into the sequestration and oxidation of heavy metals mediated by Mn(II) oxidizing microorganisms. It might be helpful to understand the geochemical fate of heavy metals in the aquatic environment and the process of microbial-mediated water self-purification.
Background
The demand for designing a new technology that can emphasize the complete removal of heavy metals increased as a result of the industrial revolution. Bioremediation was found to have a potent impact on the degradation of organic and inorganic environmental pollutants.
Main body
Bioremediation is a multidisciplinary technology that possesses safe, efficient, and low-cost characteristics. Also, one of the important features of bioremediation technology is the in-situ treatment which reduces the possibility of transmitting the contaminants to another site. The application of genetic engineering, to engineer a microorganism to acquire the ability to remove different types of heavy metals at a time or to generate a transgenic plant, is considered one of the new promising bioremediation approaches.
Short conclusion
Removal of heavy metal pollution still represents a big challenge for ecologists that’s why this review shed some light on bioremediation technology; its importance, mechanism of action, and prospects.
Tellurium (Te) is an emerging contaminant and its chemical transformation in the environment is strongly influenced by microbial processes. In this study, we investigated the adsorption of tellurite [Te(IV), TeO32-] onto the common soil bacterium Bacillus subtilis. Thiol-blocking experiments were carried out to investigate the role of cell surface sulfhydryl sites in tellurite binding, and extended X-ray absorption fine structure (EXAFS) spectroscopy was performed to determine the chemical speciation of the adsorbed tellurite. The results indicate that tellurite reacts with sulfhydryl functional groups in the extracellular polymeric substances (EPS) produced by B. subtilis. Upon binding to sulfhydryl sites in the EPS, the Te changes from Te-O bonds to Te-S coordination. Further analysis of the surface-associated molecules shows that the EPS of B. subtilis contain proteins. Removal of the proteinaceous EPS dramatically decreases tellurite adsorption and the sulfhydryl surface site concentration. These findings indicate that sulfhydryl binding in EPS plays a key role in tellurite adsorption on bacterial surfaces.
In the last years, increasing the population growth followed by an acceleration of the industrial process costs the quality of our ecosystem. Large waste quantities of industrial activities deposit risk concentrations of toxic materials like heavy metals. Heavy metal pollution has been distinguished as serious contaminants with worldwide risk since the industrial modern revolution. Environment depositions of these contaminants intimidate all the biological life forms for its high toxic characteristics. Chemical, physical, and mechanical strategies proved its low efficiency for its high energy needs, high costs, and even leave other secondary wastes to pass through the environment that raising another contaminant issue. Bioremediation through biological scavenging of heavy metals by microorganisms offers simple, low costs, low energy, and eco-friendly strategy for heavy metal elimination. Microorganisms developed extracellular (adsorption) and intracellular (accumulation) ways to bind metal ions through its viable or dead cells in a magnificent biosorption strategy. These strategies prop up as natural cell self-defense mechanisms for the elimination of the toxic effect of these hazardous materials. The whole bioremediation practicability affected by diverse factors such as microbial strain sensitivity, biomass concentricity, pH, surrounded temperature, and many else agents controls the metal ion bioavailability and the fast speed of the biosorption process.
As society transitions to low-carbon, renewable energy resources, the demand for metals and minerals is set to increase. Massive quantities of base metals and mineral materials (for example, silica and concrete) along with smaller quantities of precious metals will be required for the construction of wind turbines, solar panels and battery storage facilities to meet the demands of the ‘Electric Planet’ of the future. Harnessing microbe-mineral-metal interactions may offer many opportunities to improve some mining practises and support the long-term sustainability of mining. As easily exploitable, high-grade deposits are becoming increasingly depleted there is a need for new technologies to improve exploration and mining strategies. Microorganisms are ubiquitous and diverse, surviving in almost all environments in the Earth's crust and recent advances in molecular techniques have enabled scientists to study these communities is extraordinary detail. Microorganisms also interact directly with their environment; both responding to and changing the environment around them. These responses and their influences on the surrounding environment are preserved within their genome (a complete set of the DNA of the microorganism). Here, we discuss using state-of-the-art sequencing techniques to identify key microbial genes that have been demonstrated to correlate with metal concentrations. These genetic-based bioindicators may provide additional tools to guide and improve the success rate of mineral exploration programmes. Advances in molecular techniques will also improve existing biohydrometallurgical techniques and expand the commodity range for which biohydrometallurgy are currently economically viable. Finally, microorganisms may be used in a number of strategies for mine remediation; specifically, we review in detail microbially accelerated carbon capture and storage strategies and mine waste stabilisation.
Transmission electron microscopy of Pseudomonas putida-birnessite assemblage. Made by cryofixation freezed substitution (picture made by Naomi Dumas & Celine Loussert) Maîtrise universitaire ès Sciences en biogéosciences | June-2014 www.biogeosciences.ch Foreword This work is organized in one main chapter which represented the first version of a manuscript already formatted for a paper submission for Environment Science & Technology conformed to the journal guide. Additionally, several appendix or supplementary materials are present and offers detailed concepts, methods, results and raw data to the reader. All results present in appendices constitute some important step in our work or in some case support to our colleague. Because the appendix, accepted some case (raw data and computing script), are organized similar than a paper format, the reader can be have the bad impression to have already read this. Sorry for this disagreement. We have tried as much as possible to prevent this by making shorter introduction in the appendix. The previous goal define in our master proposal was to "asses the influence of extracellular polymeric substances (EPS) on nickel sorption of manganese oxides (MnO 2) produced by bacteria and fungy". The appendix A1, present the development of the Infra-red spectroscopy (FTIR) approach in order to asses qualitatively the functional group responsible to the Ni sorption on the biomass or the interaction between the MnO 2 and the biomass. The appendix A2, present a methodological approach to remove the EPS in order to have a more simple assemblage for assessing the influence of EPS on the sorption process. These two methodological approaches were unsuccessful performed during our master for different reasons explain in the appendix. Consequently, our main objective were refocused on a comparison of the sorption reactivity on birnessite produced bacteria or fungy. Divers microscopy work on transmission electron microscopy (TEM) performed by Dr. C. Loussert on our sample were presented on the appendix A3 together with several surprising observation about bacteria physiology. On the early stage of our research, this methodological development was a key to make a visual confirmation of the removal extracellular polymeric substance (EPS) performed in appendix A2. This appendix show also the first test of N. Dumas in order to show the interface between mineral and bacteria. During our internship at the North Carolina State University(NCSU), divers identifications (DNA and morphology) and characterization (growth rate and manganese oxidation rate) necessary to performed the sorption experiment were made on some environmental fungi. Moreover some extract works on this topic were performed for the ongoing work or with Dr. Terrence Gardner. Both of them are presented on the appendix A4. The appendix A5 constitutes two original R script used during our research witch serve as a usefull tool for our collegue. The appendix A6 constitutes a presented poster in 57th
In this study, we examined two effects on bacterial surface sulfhydryl site concentrations and distributions: (1) the effect of glucose concentration on the distribution of sulfhydryl sites between the bacterial cell surface and surface-associated extracellular polymeric substance (EPS) molecules, and (2) the effect of electron donor identity and concentration on sulfhydryl site concentrations on bacterial biomass. In each set of experiments, the total site concentration was measured using a potentiometric titration approach, and sulfhydryl site concentrations were determined using a site-specific blocking technique. The measurements were conducted with and without the removal of cellular EPS. For the first set of experiments, our results indicate that the two Gram-positive bacterial species, Bacillus subtilis, and Bacillus licheniformis, and one of the Gram-negative bacterial species studied, Pseudomonas putida, each have a greater concentration of sulfhydryl sites on their EPS molecules than is present on their cell surfaces, possibly serving to sequester toxic metals away from the cell surface. Conversely, for the Gram-negative bacterial species Shewanella oneidensis, the concentration of sulfhydryl sites on the cell surface is greater than that on its EPS molecules. S. oneidensis can gain metabolic energy through metal reduction, and hence enhancing the extent of metal binding to the cell wall through the formation of sulfhydryl binding sites may be more beneficial than the risk of metal toxicity. In the second set of experiments, increasing the concentration of two electron donors, pyruvate and glucose, in the growth medium of B. subtilis led to an increase in the percentage of total sites represented by sulfhydryl sites, but the concentration of the two other electron donors, glycerol and fumarate, had no effect on the percentage of sulfhydryl sites. Our results indicate that both the identity and the concentration of electron donors significantly influence the formation of sulfhydryl binding sites on bacterial cell surfaces. In addition, our results suggest that the total energy availability of a specific electron donor-bacterial species pairing affects both the ability of bacterial cells to produce sulfhydryl binding sites, and the distribution of those sites between the cell surface and its associated EPS molecules.
Schwertmannite was widely used to control the mobility and bioavailability of heavy metals. However, controllable biosynthesis of schwertmannite through a mild way is challenging. The objective of this research is to systematically investigate the feasibility of controllable biosynthesis of nanoscale schwertmannite through aluminum modification and evaluates the removal efficiency and mechanism of heavy metals. The results showed that Fe(II) oxidizing and biosynthesis ability of Acidithiobacillu ferrooxidans was not inhibited by Al(III) ions. Directional regulation of the morphology, structure, and functional groups of schwertmannite was revealed in the controllable biosynthesis system. Schwertmannite transformed to nanoscale wire in the Fe/Al ratio 15:30 condition, but the phase and crystal structure remain unchanged. Al (III) modification effectively enhanced the content of hydroxyl groups and sulfate in schwertmannite and the adsorption reactivity. The highest adsorption capacity toward Cu (II)/Cr(VI) reached 53.82/87.26 in schwertmannite biosynthesized with Fe/Al ratio 15/30. In addition, biosynthetic schwertmannite possess deep removal capacity toward low concentration metals and selective adsorption capacity to complex metals. Heavy metals adsorbed on schwertmannite through cation exchange, surface complexation and ligand exchange. This research is of great significance for in deep understanding of material biosynthesis and the application of waste water treatment.
Simultaneous overabundance and scarcity of inorganic phosphate (Pi) is a critical issue driving the development of innovative water/wastewater treatment technologies that not only facilitate Pi removal to prevent eutrophication, but also recover Pi for agricultural reuse. Here, a cell-surface expressed high-affinity phosphate binding protein (PstS) system was developed, and its Pi capture and release potential was evaluated. E. coli was genetically modified to express PstS on its outer membrane using the ice nucleation protein (INP) as an anchoring motif. Verification of protein expression and localization were performed utilizing SDS-polyacrylamide gel electrophoresis (SDS-PAGE), western blot, and outer membrane separation analyses. Cell surface characterization was investigated through acid-base titration, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). These tests provided information on the macromolecular structure and composition of the bacteria surface as well as the proton-exchange properties of the surface functional groups (i.e., pKa values). Phosphate desorption and adsorption batch experiments were conducted to evaluate the effects of temperature, pH, and ionic strength on phosphate capture and release. The PstS surface-displayed cells demonstrated greater potential to release and capture phosphate compared to non-modified cells. Higher temperatures up to 40°C, basic pH conditions (pH = 10.5), and higher ionic strength up to 1.0 mol/L KCl promoted 20%-50% higher phosphate release.
The goal in this study is to enhance the efficiency of bacterial extracellular electron transfer (EET) in Shewanella. oneidensis MR-1 by enhancing adhesion to the electrode. Our results clearly show a major difference in attachment and behavior of S. oneidensis MR-1 for Ca ²⁺ , Pb ²⁺ , Cd ²⁺ , and Mg ²⁺ compared to the control. The final microbial coverage, as measured by confocal microscopy and cathodic peak charge in cyclic voltammetry (Q pc ), increases with increasing metal ion concentrations. We found the cells attached to the electrode increased more with the addition of metal ion concentrations in the following order of metals: Ca ²⁺ > Pb ²⁺ > Cd ²⁺ > Mg ²⁺ compared to the control.
Riboflavin production and glucose consumption mirrored the same order as the electrochemical results.
Cambridge Core - Geochemistry and Environmental Chemistry - Analytical Geomicrobiology - edited by Janice P. L. Kenney
Many base metals and a few precious metals as well as some metalloids can be enzymatically or non-enzymatically concentrated
and dispersed by microbes in their environment. Some of these activities are commercially exploited or have a potential for
it. This article summarizes these activities and the commercial or potentially commercial use of some of them.
The local atomic environment of Cd bound to the cell wall of the gram-positive bacterium Bacillus subtilis was determined by X-ray absorption fine structure (XAFS) spectroscopy. Samples were prepared at six pH values in the range 3.4 to 7.8, and the bacterial functional groups responsible for the adsorption were identified under each condition. Under the experimental Cd and bacterial concentrations, the spectroscopy results indicate that Cd binds predominantly to phosphoryl ligands below pH 4.4, whereas at higher pH, adsorption to carboxyl groups becomes increasingly important. At pH 7.8, we observe the activation of an additional binding site, which we tentatively ascribe to a phosphoryl site with smaller Cd-P distance than the one that is active at lower pH conditions. XAFS spectra of several cadmium acetate, phosphate, and perchlorate solutions were measured and used as standards for fingerprinting, as well as to assess the ability of FEFF8 and FEFFIT to model carboxyl, phosphoryl, and hydration environments, respectively. The results of this XAFS study in general corroborate existing surface complexation models; however, some binding mechanism details could only be detected with the XAFS technique.
X-ray absorption fine structure (XAFS) measurements was used at the U L3-edge to directly determine the pH dependence of the cell wall functional groups responsible for the absorption of aqueous UO22+ to Bacillus subtilis from pH 1.67 to 4.80. Surface complexation modeling can be used to predict metal distributions in water–rock systems, and it has been used to quantify bacterial adsorption of metal cations. However, successful application of these models requires a detailed knowledge not only of the type of bacterial surface site involved in metal adsorption/desorption, but also of the binding geometry. Previous acid-base titrations of B. subtilis cells suggested that three surface functional group types are important on the cell wall; these groups have been postulated to correspond to carboxyl, phosphoryl, and hydroxyl sites. When the U(VI) adsorption to B. subtilis is measured, observed is a significant pH-independent absorption at low pH values (<3.0), ascribed to an interaction between the uranyl cation and a neutrally charged phosphoryl group on the cell wall. The present study provides independent quantitative constraints on the types of sites involved in uranyl binding to B. subtilis from pH 1.67 to 4.80. The XAFS results indicate that at extremely low pH (pH 1.67) UO22+ binds exclusively to phosphoryl functional groups on the cell wall, with an average distance between the U atom and the P atom of 3.64 ± 0.01 Å. This U-P distance indicates an inner-sphere complex with an oxygen atom shared between the UO22+ and the phosphoryl ligand. The P signal at extremely low pH value is consistent with the UO22+ binding to a protonated phosphoryl group, as previously ascribed. With increasing pH (3.22 and 4.80), UO22+ binds increasingly to bacterial surface carboxyl functional groups, with an average distance between the U atom and the C atom of 2.89 ± 0.02 Å. This U-C distance indicates an inner-sphere complex with two oxygen atoms shared between the UO22+ and the carboxyl ligand. The results of this XAFS study confirm the uranyl-bacterial surface speciation model.
Heptosyltransferase I, encoded by therfaC(waaC) gene of Escherichia coli, is thought to addl-glycero-d-manno-heptose to the inner 3-deoxy-d-manno-octulosonic acid (Kdo) residue of the lipopolysaccharide core. Lipopolysaccharide isolated from mutants defective in rfaC lack heptose and all other sugars distal to heptose. The putative donor, ADP-l-glycero-d-manno-heptose, has never been fully characterized and is not readily available. In cell extracts, the analog ADP-mannose can serve
as an alternative donor for RfaC-catalyzed glycosylation of the acceptor, Kdo2-lipid IVA. Using a T7 promoter construct that overexpresses RfaC ∼15,000-fold, the enzyme has been purified to near homogeneity. NH2-terminal sequencing confirms that the purified enzyme is the rfaC gene product. The subunit molecular mass is 36 kDa. Enzymatic activity is dependent upon the presence of Triton X-100 and
is maximal at pH 7.5. The apparentK
m (determined at near saturating concentrations of the second substrate) is 1.5 mm for ADP-mannose and 4.5 μm for Kdo2-lipid IVA. Chemical hydrolysis of the RfaC reaction product at 100 °C in the presence of sodium acetate and 1% sodium dodecyl sulfate
generates fragments consistent with the inner Kdo residue of Kdo2-lipid IVA as the site of mannosylation. The analog, Kdo-lipid IVA, functions as an acceptor, but is mannosylated at less than 1% the rate of Kdo2-lipid IVA. The purified enzyme displays no activity with ADP-glucose, GDP-mannose, UDP-glucose, or UDP-galactose. Mannosylation of
Kdo2-lipid IVA catalyzed by RfaC proceeds in high yield and may be useful for the synthesis of lipopolysaccharide analogs. Pure RfaC can
also be used together with Kdo2-[4′-32P]lipid IVA to assay for the physiological donor (presumably ADP-l-glycero-d-manno-heptose) in a crude, low molecular weight fraction isolated from wild type cells.
An analysis of the Pseudomonas aeruginosa genomic sequence revealed three gene clusters, PA1381-1393, PA2231-2240, and PA3552-3558, in addition to the alginate biosynthesis
gene cluster, which appeared to encode functions for exopolysaccharide (EPS) biosynthesis. Recent evidence indicates that
alginate is not a significant component of the extracellular matrix in biofilms of the sequenced P. aeruginosa strain PAO1. We hypothesized that at least one of the three potential EPS gene clusters revealed by genomic sequencing is
an important component of P. aeruginosa PAO1 biofilms. Thus, we constructed mutants with chromosomal insertions in PA1383, PA2231, and PA3552. The mutant with a
PA2231 defect formed thin unstructured abnormal biofilms. The PA3552 mutant formed structured biofilms that appeared different
from those formed by the parent, and the PA1383 mutant formed structured biofilms that were indistinguishable from those formed
by the parent. Consistent with a previous report, we found that polysaccharides were one component of the extracellular matrix,
which also contained DNA. We suggest that the genes that were inactivated in our PA2231 mutant are required for the production
of an EPS, which, although it may be a minor constituent of the matrix, is critical for the formation of P. aeruginosa PAO1 biofilms.
In order to clarify the role of picocyanobacteria in aquatic biogeochemical processes (e.g., calcite precipitation), cell surface properties need to be investigated. An experimental study of the cell surface characteristics of two Synechococcus-type unicellular autotrophic picocyanobacterial strains was carried out. One strain was isolated from Lake Plon and contained phycocyanin, the other strain came from Lago Maggiore and was rich in phycoerythrin. Potentiometric titrations were conducted to determine the different types of sites present on the bacteria cell walls. Infrared spectroscopy allowed characterization of the various functional groups (RNH(2), RCOOH, ROH, RPO(2)) and investigations of zeta potential provided insight into the isoelectrical points of the strains. Titrations reveal three distinct sites on the bacterial surfaces of phycocyanin- and phycoerythrin-rich strains with pK values of 4.8+/-0.3/5.0+/-0.2, 6.6+/-0.2/6.7+/-0.4, and 8.8+/-0.1/8.7+/-0.2, corresponding to carboxyl, phosphate, and amine groups with surface densities of 2.6+/-0.4/7.4+/-1.6 x 10(-4), 1.9+/-0.5/4.4+/-0.8 x 10(-4), and 2.5+/-0.4/4.8+/-0.7 x 10(-4) mol/g of dry bacteria. The deprotonation constants are similar to those of bacterial strains and site densities are also within an order of magnitude of other strains. The phycoerythrin-rich strain had a higher number of binding sites than the phycocyanin-rich strain. The results showed that picocyanobacteria may adsorb either calcium cations or carbonate anions and therefore strongly influence the biogeochemical cycling of calcite in pelagic systems.
Microbial extracellular polymeric substances (EPS) are the key components for the aggregation of microorganisms in biofilms, flocs and sludge. They are composed of polysaccharides, proteins, nucleic acids, lipids and other biological macromolecules. EPS provide a highly hydrated gel matrix in which microbial cells can establish stable synergistic consortia. Cohesion and adhesion as well as morphology, structure, biological function and other properties such as mechanical stability, diffusion, sorption and optical properties of microbial aggregates are determined by the EPS matrix. Also, the protection of biofilm organisms against biocides is attributed to the EPS. Their matrix allows phase separation in biofiltration and is also important for the degradation of particulate material which is of great importance for the self purification processes in surface waters and for waste water treatment. In this volume, analysis, characterization, composition, regulation, function and interactions of microbial EPS are covered.
The field of membrane biology is increasingly characterized by a major concern with the cell surface, and for good reason. The cell surface participates in an unusually wide range of biological phenomena, among them cell division, growth, differentiation, morphogenesis, antigenicity, cell recognition, and neoplastic transformation. The functions of the membrane surface are mediated by its macromolecular components. The cell surface is visualized both in its normal state and as affected by certain disease processes by means of a number of bioelectric and electrokinetic techniques. The various roles subserved by the cell surface in both these states are reviewed in relation to the available data on the characterization, organization and topographical distribution of its macromolecular components.
Aqueous metal cation adsorption onto bacterial surfaces can be successfully modeled by means of a surface complexation approach. However, relatively few stability constants for metal-bacterial surface complexes have been measured. In order to determine the bacterial adsorption behavior of cations that have not been studied in the laboratory, predictive techniques are required that enable estimation of the stability constants of bacterial surface complexes. In this study, we use a linear free-energy approach to compare previously measured stability constants for Bacillus subtilis metal-carboxyl surface complexes with aqueous metal-organic acid anion stability constants. The organic acids that we consider are acetic, oxalic, citric, and tiron. We add to this limited data set by conducting metal adsorption experiments onto Bacillus subtilis, determining bacterial surface stability constants for Co, Nd, Ni, Sr, and Zn.
Metal accumulation by solid substances can counteract metal mobilization in the environment if the solid substance is immobile. Microorganisms have a high surface area-to-volume ratio because of their small size and therefore provide a large contact area that can interact with metals in the surrounding environment. Microbial metal accumulation has received much attention in the last years due to the potential use of microorganisms for cleaning metal-polluted water. However, considerably less attention has been paid to the role of microorganisms for metal mobility in soil even though the same processes may occur there. Therefore, this paper highlights this area. The different accumulation processes that microorganisms perform are analyzed and their potential significance in soil systems is discussed.
Fungal cell walls possess strong complexing properties, which make them valuable biosorbents to remove heavy metals from wastewaters. The binding mechanisms of Zn and Pb to Penicillium chrysogenum cell walls have been studied by solution chemistry and extended X-ray absorption fine structure (EXAFS) spectroscopy as a function of the complexation rate. It is shown that Zn and Pb bind to the predominant phosphoryl (≈95%) and minor carboxyl groups (≈5%) with a reversed affinity. Zn is predominantly complexed to four PO4 groups in a tetrahedral configuration at low (7.6 × 10-3 mmol/g) to high (0.15 mmol/g) Zn concentration and additionally to COOH groups at total saturation of reactive sites (0.22 mmol/g). In contrast, carboxyl complexes of Pb ((COO)n−Pb) are formed at low Pb concentration (5.6 10-3 mmol/g), and their formation is followed by (PO4)n−Pb complexes at higher complexation rate. The difference in complexation affinity by reactive PO4 and COOH groups observed by EXAFS provides a molecular level explanation for the differences in Pb and Zn isotherms. The Pb isotherm exhibits two plateaus, which correspond to the successive saturation of COOH and PO4 sites, whereas the Zn isotherm has a single-site Langmuir shape because low affinity minor (COO)n−Zn complexes formed at high metal concentration are masked by more abundant (PO4)4−Zn complexes, which readily form.
Thermodynamic parameters for proton and metal adsorption onto a gram-negative bacterium from the genus Enterobacteriaceae have been determined and compared with parameters for other strains of bacteria. Potentiometric titrations were used to determine the different types of sites present on bacterial cell walls. Stability constants for adsorption of Pb, Cu and Zn to specific sites were determined from batch adsorption experiments at varying pH with constant metal concentration. Titrations revealed 3 distinct acidic surface sites on the bacterial surface, with pK values of 4.3±0.2, 6.9±0.5 and 8.9±0.5, corresponding to carboxyl, phosphate and hydroxyl/amine groups, with surface densities of 5.0±0.7×10−4, 2.2±0.6×10−4 and 5.5±2.2×10−4 mol/g of dry bacteria. Only carboxyl and phosphate sites are involved in metal uptake, yielding the following intrinsic stability constants: Log Kcarboxyl: Zn=3.3±0.1, Pb=3.9±0.8, and Cu=4.4±0.2, Log Kphosphoryl: Zn=5.1±0.1 and Pb=5.0±0.9. The deprotonation constants are similar to those of other strains of bacteria, while site densities are also within an order of magnitude of other strains. The similarities in surface chemistry and metal stability constants suggest that bacteria may be represented by a simple generic thermodynamic model for the purposes of modelling metal transport in natural environments. Comparison with oxide-coated sand shows that bacteria can attenuate some metals to much lower pH values.
In order to test the ability of a surface complexation approach to account for metal-bacteria interactions in near surface fluid-rock systems, we have conducted experiments that measure the extent of adsorption in mixed metal, mixed bacteria systems. This study tests the surface complexation approach by comparing estimated extents of adsorption based on surface complexation modeling to those we observed in the experimental systems. The batch adsorption experiments involved Ca, Cd, Cu, and Pb adsorption onto the surfaces of 2 g positive bacteria: Bacillus subtilis and Bacillus licheniformis. Three types of experiments were performed: 1. Single metal (Ca, Cu, Pb) adsorption onto a mixture of B. licheniformis and B. subtilis; 2. mixed metal (Cd, Cu, and Pb; Ca and Cd) adsorption onto either B. subtilis or B. licheniformis; and 3. mixed or single metal adsorption onto B. subtilis and B. licheniformis. %Independent of the experimental results, and based on the site specific stability constants for Ca, Cd, Cu, and Pb interactions with the carboxyl and phosphate sites on B. licheniformis and B. subtilis determined by Fein et al. (1997), by Daughney et al. (1998) and in this study, we estimate the extent of adsorption that is expected in the above experimental systems.
The maintenance of waterways generates large amounts of dredged sediments, which are deposited on adjacent land surfaces. These sediments are often rich in metal contaminants and present a risk to the local environment. Understanding how the metals are immobilized at the molecular level is critical for formulating effective metal containment strategies such as phytoremediation. In the present work, the mineralogical transformations of Zn-containing phases induced by two graminaceous plants (Agrostis tenuis and Festuca rubra) in a contaminated sediment ([Zn] = 4700 mg kg−1, [P2O5] = 7000 mg kg−1, pH = 7.8), untreated or amended with hydroxylapatite (AP) or Thomas basic slag (TS), were investigated after two yr of pot experiment by scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS), synchrotron-based X-ray microfluorescence (μ-SXRF), and powder and laterally resolved extended X-ray absorption fine structure (μ-EXAFS) spectroscopy. The number and nature of Zn species were evaluated by principal component (PCA) and least-squares fitting (LSF) analysis of the entire set of μ-EXAFS spectra, which included up to 32 individual spectra from regions of interest varying in chemical composition. Seven Zn species were identified at the micrometer scale: sphalerite, gahnite, franklinite, Zn-containing ferrihydrite and phosphate, (Zn-Al)-hydrotalcite, and Zn-substituted kerolite-like trioctahedral phyllosilicate. Bulk fractions of each species were quantified by LSF of the powder EXAFS spectra to linear combinations of the identified Zn species spectra.
In this study, we measure the thermodynamic stability constants for proton and Cd binding onto the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, and the Gram-positive bacteria Bacillus megaturium, Streptococcus faecalis, Staphylococcus aureus, Sporosarcina ureae, and Bacillus cereus. Potentiometric titrations and Cd-bacteria adsorption experiments yield average values for the carboxyl site pKa, site concentration, and log stability constant for the bacterial surface Cd-carboxyl complex of 5.0, 2.0 × 10−3 mol/g and 4.0 respectively. Our results indicate that a wide range of bacterial species exhibit nearly identical Cd adsorption behavior as a function of pH. We propose that metal-bacteria adsorption is not dependent on the bacterial species involved, and we develop a generalized adsorption model which may greatly simplify the task of quantifying the effects of bacterial adsorption on dissolved mass transport in realistic geologic systems.
Metal ion binding to the bacterial cell wall is the first step in the interactions of a metal with a bacterium. Cadmium and zinc ion binding to isolated cell walls of Rhodococcus erythropolis A177 has been studied for a wide range of proton and calcium concentrations. The release of calcium ions and protons during metal ion binding is an indication of the competitive nature of the binding. Calculations, based on the metal binding data and the pH-dependent charging behavior, reveal that the cell wall becomes positively charged at high coverage with bivalent ions. A cooperative effect of the presence of calcium on metal ion binding was observed. Apparently, the cell wall structure is altered in the presence of bivalent ions. Since calcium is a dominant bivalent cation in most natural systems, one may regard the calcium as a ''structure determining ion''. On the basis of a qualitative interpretation of the data, the NICA model was selected for a quantitative description of the data.
Amine and carboxyl groups of the cell wall of Bacillus subtilis were chemically modified individually to neutralize their electrochemical charge for determination of their contribution to the metal uptake process. Mild alkali treatment removed ca. 94% of the constituent teichoic acid (expressed as inorganic phosphorus) and allowed estimation of metal interaction with phosphodiester bonds. Chemical modifications of amine functions did not reduce the metal uptake values as compared to native walls, whereas extraction of teichoic acid caused a stoichiometric reduction in levels. In contrast, alteration of carboxyl groups severely limited metal deposition of most of the metals tested. X-ray diffraction and electron microscopy suggested, in this case, that the form and structure of the metal deposit could be different from that found in native walls. The observations suggest that carboxyl groups provide the major site of metal deposition in the B. subtilis wall.
Many Escherichia coli strains are covered in a layer of surface-associated polysaccharide called the capsule. Capsular polysaccharides represent a major surface antigen, the K antigen, and more than 80 distinct K serotypes result from structural diversity in these polymers. However, not all capsules consist of K antigen. Some are due to production of an extensive layer of a polymer structurally identical to a lipopolysaccharide O antigen, but distinguished from lipopolysaccharide by the absence of terminal lipid A-core. Recent research has provided insight into the manner in which capsules are organized on the Gram-negative cell surface, the pathways used for their assembly, and the regulatory processes used to control their expression. A limited repertoire of capsule expression systems are available, despite the fact that the producing bacteria occupy a variety of ecological niches and possess diverse physiologies. All of the known capsule assembly systems seen in Gram-negative bacteria are represented in E. coli, as are the majority of the regulatory strategies. Escherichia coli therefore provides a variety of working models on which studies in other bacteria are (or can be) based. In this review, we present an overview of the current molecular and biochemical models for capsule expression in E. coli. By taking into account the organization of capsule gene clusters, details of the assembly pathway, and regulatory features that dictate capsule expression, we provide a new classification system that separates the known capsules of E. coli into four distinct groups.
Acid-base titration experiments and electrostatic force microscopy (EFM) were used to investigate the cell surface electrochemical heterogeneity of the Fe(III)-reducing bacteria, Shewanella putrefaciens. The acid-base titrations extended from pH 4 to 10, and the titration data were fit using a linear programming pKa spectrum approach. Overall, a five-site model accounted for the observed titration behavior with the most acidic sites corresponding to carboxylic groups and phosphodiester groups, intermediate sites phosphoryl groups, and two basic sites equivalent to amine or hydroxyl groups. The pH for the point of zero charge on the bacteria was 5.4. In EFM images of cells rinsed in solutions at pH 4.0, 7.0, and 8.0, a pronounced increase in small (< or = 100 nm diameter) high contrast patches was observed on the cells with increasing pH. The pH dependence of EFM image contrast paralleled the pattern of cell surface charge development inferred from the titration experiments; however, quantitative analysis of high contrast regions in the EFM images yielded lower surface charge values than those anticipated from the titration data. For example at pH 7, the calculated surface charge of high contrast regions in EFM images of the bacterial cells was -0.23 microC/cm2 versus -20.0 microC/cm2 based on the titration curve. The differences in surface charge estimates between the EFM images and titration data are consistent not only with charge development throughout the entire volume of the bacterial cell wall (i.e., in association with functional groups that are not directly exposed at the cell surface) but also with the presence of a thin structural layer of water containing charge-compensating counterions. In combination, the pKa spectra and EFM data demonstrate that a particularly high degree of electrochemical heterogeneity exists within the cell wall and at the cell surface of S. putrefaciens.
OmpT is an integral outer membrane protease of Escherichia coli. Overexpression of OmpT in E. coli and subsequent in vitro folding of the produced inclusion bodies yielded protein with a native-like structure. However, enzymatically active protease was only obtained after addition of the outer membrane lipid lipopolysaccharide (LPS). OmpT is the first example of an enzyme that requires LPS for activity. In this study, we investigated the nature of this activation. Circular dichroism analysis showed that binding of LPS did not lead to large structural changes. Titration of OmpT with LPS and determining the resulting OmpT activity with a fluorimetric assay yielded a dissociation constant of 10-4 m for E. coli K-12 LPS. Determining the dissociation constants for different LPS chemotypes revealed that a fully acylated lipid A part is minimally required for activation of OmpT. The heptose-bound phosphates in the inner core region were also important for activation. The affinity for LPS was not dependent on the concentration of substrate, neither was affinity for the substrate influenced by the concentration of LPS. This indicated that LPS most likely does not act at the level of substrate binding. We hypothesize that LPS induces a subtle conformational change in the protein that is required for obtaining a native active site geometry.
The surface properties of ferrihydrite were studied by combining wet chemical data, Cd(K) EXAFS data, and a surface structure and protonation model of the ferrihydrite surface. Acid-base titration experiments and Cd(II)-ferrihydrite sorption experiments were performed within 3<-log[H(+)]<10.5 and 0.5<[Cd(t)]<12 mM in 0.3 M NaClO(4) at 25 degrees C, where [Cd(t)] refers to total Cd concentration. Measurements at -5.5<or=log[Cd(t)]<or=-1.4 at fixed pH completed the wet chemical data set. The acid-base titration data could be adequately modeled by triple bond Fe- OH(2)(+1/2)-H(+)<-->triple bond Fe-OH(-1/2),logk((int))=-8.29, assuming the existence of a unique intrinsic microscopic constant, logk((int)), and consequently the existence of a single significant type of acid-base reactive functional groups. The surface structure model indicates that these groups are terminal water groups. The Cd(II) data were modeled assuming the existence of a single reactive site. The model fits the data set at low Cd(II) concentration and up to 50% surface coverage. At high coverage more Cd(II) ions than predicted are adsorbed, which is indicative of the existence of a second type of site of lower affinity. This agrees with the surface structure and protonation model developed, which indicates comparable concentrations of high- and low-affinity sites. The model further shows that for each class of low- and high-affinity sites there exists a variety of corresponding Cd surface complex structure, depending on the model crystal faces on which the complexes develop. Generally, high-affinity surface structures have surface coordinations of 3 and 4, as compared to 1 and 2 for low-affinity surface structures.
In infiltration basins, such as in any kind of porous media, bacteria may form biofilms. When conditions induce destabilization of this biofilm, resulting colloids are transported by the hydraulic flow. Some studies have focused on the role played by these bacterial colloids in pollutants transport in soil. This study deals with the ability of Pseudomonas putida to retain zinc and investigates the facilitated transport of this metal. Batch and columns experiments have been carried out. Bacteria display a great affinity for zinc in batch experiments and facilitated transport have been highlighted in a small extent, for the moment. A scenario of stabilization/destabilization of the biofilm has been designed and may be employed for further investigations.
The long- and short-term interactions between zinc, an essential but also toxic element, and freshwater and marine diatoms are not well understood partly because of a lack of information on Zn speciation on the surface and inside the cells. In this work, interactions of aqueous Zn2+ with marine (Skeletonema costatum) and freshwater (Achnanthidium minutissimum, Navicula minima, and Melosira varians) diatoms were studied using conventional macroscopic techniques, while the local atomic structure of metal ions adsorbed on their surface or incorporated into the cells was characterized by in-situ Zn K-edge X-ray absorption fine structure (XAFS) spectroscopy on both intact and liophylized samples. At the cell surface for all diatom species studied, Zn was tetrahedrally coordinated with oxygen at approximately 2.00 +/- 0.02 A and monodentately bonded to one or two carboxylate groups; these results are consistent with the surface speciation model developed from macroscopic adsorption experiments. The atomic environment of Zn incorporated into freshwater diatoms during long-term growth in normal nutrient media was distinctly differentfrom that of adsorbed Zn: it was dominated by O (and/or N) neighbors in a tetrahedral arrangement at 1.97 +/- 0.02 A in the first atomic shell, with the presence of 1 phosphorus and 2 carbons in the Zn second shell. Contrasting speciation of intracellular zinc was revealed for the marine species Skeletonema costatum in which Zn was coordinated to 2 O/N atoms and 2 sulfur groups in the form of cysteine-histidine complexes and/or zinc thiolate clusters. These new structural data strongly suggest: (i) the predominant > R-COO- ligand binding of Zn atthe diatom surface; (ii) the nonspecific storage of Zn in the form of carboxylate/phosphate groups inside the cell of freshwater species; and (iii) the highly specific thiol-ligand coordination of intracellular zinc for marine S. costatum species.
Microbial biofilms are present in soils, sediments, and natural waters. They contain bioorganic metal-complexing functional groups and are thought to play an important role in metal cycling in natural and contaminated environments. In this study, the metal-complexing functional groups present within a suspension of bacterial cell aggregates embedded in extracellular polymeric substances (EPS) were identified in Zn adsorption experiments conducted at pH 6.9 with the freshwater and soil bacterium Pseudomonas putida. The adsorption data were fit with the van Bemmelen-Freundlich model. The molecular speciation of Zn within the biofilm was examined with Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The Zn EXAFS data were analyzed by shell-by-shell fitting and linear least-squares fitting with reference spectra. Zinc sorption to the biofilm was attributed to predominantly Zn--phosphoryl (85 +/- 10 mol %) complexes, with a smaller contribution to sorption from carboxyl-type complexes (23 +/- 10 mol %). The results of this study spectroscopically confirm the importance of phosphoryl functional groups in Zn sorption by a bacterial biofilm at neutral pH.
Microbial Extracellular Polymeric SubstancessCharacterization, Structure, and Func-tion Putative exopolysaccharide synthesis genes influence Pseudomonas aeruginosa biofilm development
- J Wingender
- T Neu
- H Flemming
Wingender, J.; Neu, T.; Flemming, H., Eds. Microbial Extracellular Polymeric SubstancessCharacterization, Structure, and Func-tion; Springer-Verlag: Berlin, 1999. (31) Matsukawa, M.; Greenberg, E. P. Putative exopolysaccharide synthesis genes influence Pseudomonas aeruginosa biofilm development. J. Bacteriol. 2004, 186, 4449-4456.
EXAFS determination of Pb, Zn complexing sites of Penicillium chrysogenum cell walls
- G Sarret
- A Manceau
- L Spadini
- J C Roux
- J L Hazemann
- Y Soldo
- L Eybert-Bé
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