Figure 5 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Light micrographs of Alexandrium pacificum using differential interference contrast (A-D) and epifluorescence microscopy (Solophenyl Flavine staining) of Lugol-fixed cultured cells (E-O). (A) Ventral view with focus in the cell middle, notice the two ends of the sausage-shaped nucleus (n). (B) Light micrographs of Alexandrium pacificum using differential interference contrast (A-D) and epifluorescence microscopy (Solophenyl Flavine staining) of Lugol-fixed cultured cells (E-O). (A) Ventral view with focus in the cell middle, notice the two ends of the sausage-shaped nucleus (n). (B) Dorsal view with focus in the dorsal half of the cell showing the path of the nucleus (n). (C) Antapical view with focus in the cell middle, notice the sausage-shaped nucleus (n) dorsally. (D) Dorsal view with focus on the peripherally located, elongated chloroplasts. (E) General cell shape. (F-H) Ventral view showing the shapes of the first apical (1 ) and sixth precingular (6 ) plates. Note the different degree of asymmetry in 1 . (I,J) Ventral views of squeezed thecae showing the thecal plates. (K) Doral view of a squeezed theca showing the thecal plates. (L) Ventral to antapical view showing sulcal plates. (M) Sulcal plates. (N) Ventral epithecal view showing the shapes of characteristic plates 1 , 6 , and anterior sulcal plate (Sa). (O) The first apical plate (1 ) with ventral pore (arrow). Scale bars = 10 µm.
Source publication
In 2016, 2017 and 2018, elevated levels of the species Alexandrium pacificum were detected within a blue mussel (Mytilus galloprovincialis) aquaculture area at Twofold Bay on the south coast of New South Wales, Australia. In 2016, the bloom persisted for at least eight weeks and maximum cell concentrations of 89,000 cells L−1 of A. pacificum were r...
Similar publications
Across the European Atlantic Arc (Scotland, Ireland, England, France, Spain, and Portugal) the shellfish aquaculture industry is dominated by the production of mussels, followed by oysters and clams. A range of spatially and temporally variable harmful algal bloom species (HABs) impact the industry through their production of biotoxins that accumul...
Citations
... The dinoflagellate Alexandrium is an armored photosynthetic microeukaryote and is widely distributed in worldwide coastal waters (Band-Schmidt et al. 2019; Barua et al. 2020). Within the genus, more than 34 species have been described morphologically (Guiry and Guiry 2021), and at least 14 species are known to form harmful algal blooms (HABs). ...
The marine dinoflagellate Alexandrium is known to produce saxitoxins (STXs), causing paralytic shellfish poisoning (PSP). STX biosynthesis is catalyzed by eight enzymes encoded in their corresponding sxt core genes. SxtU encodes a short-chain dehydrogenase that participates in the last step of the STX synthesis; however, its characteristics are insufficiently elucidated in toxic dinoflagellates. Herein, we characterized the full-length sxtU from the toxic Alexandrium pacificum and evaluated its transcriptional responses under varying salinity and temperature. The ApsxtU cDNA was 936 bp in length, comprising an 819-bp open reading frame (68.9% GC). The 3-dimensional structure contained the Rossmann fold with seven β-sheets and eight α-helices in each monomer. Phylogenetic analysis showed that ApsxtU formed a clade with that of Alexandrium tamarense and toxic cyanobacteria. In the tested conditions, STX eq of A. pacificum was the highest in the exponential phase at 16 °C (96.27 fmol cell⁻¹), at 33 psu (59.67 fmol cell⁻¹), and decreased at other conditions. ApsxtU expression levels increased in time and reached the highest in the stationary phase at 40 psu but were not statistically correlated with toxin contents. These suggest that sxtU may be involved in STXs synthesis and also in other metabolic functions in dinoflagellates.
... In addition, we compared the relationship between salinity and toxin content through transcriptional regulation. The test species A. pacificum (formerly A. tamarense) is known to produce STXs [13,24] and is widely distributed in the coastal waters of Europe, Australia, Asia, and America [43][44][45][46][47]. In Korea, the species was first recorded in 1985 [48], and it has been continuously investigated in terms of environmental monitoring and toxicity because of its early spring blooms and toxin outbreaks [49,50]. ...
Salinity is an important factor for regulating metabolic processes in aquatic organisms; however, its effects on toxicity and STX biosynthesis gene responses in dinoflagellates require further elucidation. Herein, we evaluated the physiological responses, toxin production, and expression levels of two STX synthesis core genes, sxtA4 and sxtG, in the dinoflagellate Alexandrium pacificum Alex05 under different salinities (20, 25, 30, 35, and 40 psu). Optimal growth was observed at 30 psu (0.12 cell division/d), but cell growth significantly decreased at 20 psu and was irregular at 25 and 40 psu. The cell size increased at lower salinities, with the highest size of 31.5 µm at 20 psu. STXs eq was highest (35.8 fmol/cell) in the exponential phase at 30 psu. GTX4 and C2 were predominant at that time but were replaced by GTX1 and NeoSTX in the stationary phase. However, sxtA4 and sxtG mRNAs were induced, and their patterns were similar in all tested conditions. PCA showed that gene transcriptional levels were not correlated with toxin contents and salinity. These results suggest that A. pacificum may produce the highest amount of toxins at optimal salinity, but sxtA4 and sxtG may be only minimally affected by salinity, even under high salinity stress.
... The optimum water temperature of the cultured strains of A. pacificum from the East and South China Sea was 20 and 23 • C, respectively, similar to strains from Japan, Korea, Australia, and the Mediterranean Sea, showing optimum growth temperatures from 20 • C to 25 • C [4,22,23,27,56]. Strain TIO855 from the Yellow Sea showed lower division rates (0.06 divisions d −1 ) at 29 • C compared to the 0.34 divisions d -1 of the South China Sea strain TIO866, suggesting that geographically separated populations are adapted to local environments. ...
The dinoflagellate Alexandrium pacificum can produce paralytic shellfish toxins and is mainly distributed in the Pacific. Blooms of A. pacificum have been frequently reported in offshore areas of the East China Sea, but not along the coast. To investigate the bloom dynamics of A. pacificum and their potential origins in the Taiwan Strait, we performed intensive sampling of both water and sediments from 2017 to 2020. Ellipsoidal cysts were identified as A. pacificum and enumerated based on microscopic observation. Their abundances were quite low but there was a maximum of 9.6 cysts cm−3 in the sediment near the Minjiang River estuary in May 2020, consistent with the high cell abundance in the water column in this area. Cells of A. pacificum were examined using a quantitative polymerase chain reaction, and they appeared to be persistent in the water column across the seasons. High densities of A. pacificum (103 cells L−1) were observed near the Jiulongjiang and Minjiang River estuary in early May 2020, where high nutrients (dissolved inorganic nitrogen and phosphate), and relatively low temperatures (20–21 °C) were also recorded. Strains isolated from the East and South China Sea exhibited the highest division rate (0.63 and 0.93 divisions d−1) at 20 and 23 °C, respectively, but the strain from the Yellow Sea showed the highest division (0.40 divisions d−1) at 17–23 °C. Strains from the East and South China Sea shared similar toxin profiles dominated by the N-sulfocarbamoyl toxins C1/2, but the strain from the Yellow Sea predominantly produced the carbamoyl toxins GTX1/4 and no C1/2. Our results suggest that both cyst germination and persistent cells in the water column might contribute to the bloom formation in the Taiwan Strait. Our results also indicate that the East and South China Sea populations are connected genetically through similar toxin formation but separated from the Yellow Sea population geographically.
... While the genomic region targeted for an assay is frequently a molecular barcoding region, usually part of the rRNA operon such as ITS, LSU or the small subunit (SSU) rRNA, the qPCR assay developed for paralytic shellfish toxin producing species, targets a functional gene that controls PST toxin biosynthesis, sxtA4 (Murray et al., 2011). This methodology was used to confirm the presence of Alexandrium pacificum as the causative species in an unprecedented paralytic shellfish toxin bloom event in Twofold Bay, SE Australia during 2016 (Barua, 2020). ...
Harmful algal blooms, including those caused by the toxic diatom Pseudo-nitzschia, can have significant impacts on human health, ecosystem functioning and ultimately food security. In the current study we characterized a bloom of species of Pseudo-nitzschia that occurred in a south-eastern Australian oyster-growing estuary in 2019. Using light microscopy, combined with molecular (ITS/5.8S and LSU D1-D3 rDNA regions) and toxicological evidence, we observed the bloom to consist of multiple species of Pseudo-nitzschia including P. cf. cuspidata, P. hasleana, P. fraudulenta and P. multiseries, with P. cf. cuspidata being the only species that produced domoic acid (3.1 pg DA per cell). As several species of Pseudo-nitzschia co-occurred, only one of which produced DA, we developed a rapid, sensitive and efficient quantitative real-time polymerase chain reaction (qPCR) assay to detect only species belonging to the P. pseudodelicatissima complex Clade I, to which P. cf. cuspidata belongs, and this indicated that P. cuspidata or closely related strains may have dominated the Pseudo-nitzschia community at this time. Finally, using high resolution water temperature and salinity sensor data, we modeled the relationship between light microscopy determined abundance of P. delicatissima group and environmental variables (temperature, salinity, rainfall) at two sites within the estuary. A total of eight General Linear Models (GLMs) explaining between 9 and 54% of the deviance suggested that the temperature (increasing) and/or salinity (decreasing) data were generally more predictive of high cell concentrations than the rainfall data at both sites, and that overall, cell concentrations were more predictive at the more oceanic site than the more upstream site, using this method. We conclude that the combination of rapid molecular methods such as qPCR and real-time sensor data modeling, can provide a more rapid and effective early warning of harmful algal blooms of species of Pseudo-nitzschia, resulting in more beneficial regulatory and management outcomes.
... Along the Korean coastal waters, A. pacificum showed seasonal patterns of population abundance, usually with a higher abundance from April to July, when the water temperature was between 16°C and 23°C (Mok et al., 2013). In another case, the cell densities reported during the bloom events of A. pacificum at Twofold Bay on the south coast of Australia are quite variable, ranging from 1.2 × 10 3 cells L −1 to 8.9 × 10 4 cells L −1 (Barua et al., 2020). In addition to A. pacificum, blooms of the toxic dinoflagellate A. catenella occurred in the spring and autumn during the last decade in many coastal waters including Chile, New Zealand, and the western Mediterranean Sea (with up to 1.5 × 10 7 cells L −1 detected in the autumn of 2004) (Lilly et al., 2002;Penna et al., 2005;Genovesi et al., 2011). ...
... Then, the cells may release the STXs to aquatic systems, along with the existing toxins produced by other early dominant toxigenic species, subsequently leading to the contamination or the mortality of fish and shellfish, as well as other marine animals (Fig. 5). This was supported by previous surveys reporting that PSP toxins were detected in mussels and bivalves collected from Korea when the water temperature ranged from 8.2°C to 15.0°C (Mok et al., 2013;Barua et al., 2020). In contrast, during summer or autumn, the A. pacificum cells did not produce many STXs and showed little or no effect on other marine organisms (Fig. 5), which could explain why low levels of STXs were detected in STXproducing species blooming in temperate coastal waters (Lim et al., 2007). ...
Temperature may affect the production of saxitoxin (STX) and its derivatives (STXs); however, this is still controversial. Further, STX-biosynthesis gene regulation and the relation of its toxicity with temperature are not clearly understood. In the present study, we evaluated the effects of different temperatures (12 °C, 16 °C, and 20 °C) on the growth, toxin profiles, and expression of two core STX-biosynthesis genes, sxtA and sxtG, in the toxic dinoflagellate Alexandrium pacificum Alex05, isolated from Korean coasts. We found that temperature significantly affected cell growth, with maximum growth recorded at 16 °C, followed by 20 °C and 12 °C. HPLC analysis revealed mostly 12 of STXs from the tested cultures. Interestingly, the contents of STXs increased in the cells cultured at 16 °C and exposed to cold stress, compared to the 20 °C culture and heat stress; however, toxin components were much more diverse under heat stress. These toxin profiles generally matched with the sxtA and sxtG expression levels. Incubation at lower temperatures (12 °C and 16 °C) and exposure to cold stress increased sxtA and sxtG expressions in the cells, whereas heat stress showed little change or downregulated the transcription of both genes. Principal component analysis (PCA) showed low correlation between STXs eq and expressional levels of sxtA and sxtG in heat-stressed cells. These results suggest that temperature might be a crucial factor affecting the level and biosynthesis of STXs in marine toxic dinoflagellates.
... This was followed by another PST event in 2017 where concentrations reached 150 mg/kg PST in mussels, 22 mg/kg in oysters, 11 mg/kg in lobster and 1.3 mg/kg in abalone viscera (Dorantes-Aranda et al., 2018). PST events have also been a recent phenomenon along the New South Wales coast with elevated levels of Alexandrium pacificum occurring in 2016, 2017 and 2018 (Barua et al., 2020). ...
Paralytic shellfish toxin (PST) events are often difficult to predict because synergistic processes, involving multiple temporal and spatial scales, are responsible for their development. In this study, we consider a suite of factors, from local to regional processes, driving paralytic shellfish toxin (PST) events associated with Alexandrium catenella on the east coast of Tasmania (Australia). PST concentrations in shellfish were compared against environmental variables, including daily wind speed and direction, satellite chlorophyll-a, sea surface temperature and river discharge. Relationships were tested using generalized linear models (GLMs). GLM coefficients confirm that high PST events were significantly favored by cooler temperatures and higher chlorophyll-a concentrations. PST were seasonal, occurring between August and November and showed a significant relationship with sustained coastal upwelling and wind transition events after one to three months of predominantly upwelling winds. Satellite imagery shows evidence of cross shelf transport moderating PST events. Overall, the results suggest that a combination of factors (currents, upwelling conditions and changes in sea surface temperature) work together to initiate and moderate PST events. The use of GLMs provides a useful tool for understanding synergistic relationships. These techniques are of value for developing reliable predictive models to forecast and manage the effects of harmful and costly PST events.
Marine toxins produced by marine organisms threaten human health and impose a heavy public health burden on coastal countries. Lately, there has been an emergence of marine toxins in regions that were previously unaffected, and it is believed that climate change may be a significant factor. This paper systematically summarizes the impact of climate change on the risk of marine toxins in terms of changes in seawater conditions. From our findings, climate change can cause ocean warming, acidification, stratification, and sea-level rise. These climatic events can alter the surface temperature, salinity, pH, and nutrient conditions of seawater, which may promote the growth of various algae and bacteria, facilitating the production of marine toxins. On the other hand, climate change may expand the living ranges of marine organisms (such as algae, bacteria, and fish), thereby exacerbating the production and spread of marine toxins. In addition, the sources, distribution, and toxicity of ciguatoxin, tetrodotoxin, cyclic imines, and microcystin were described to improve public awareness of these emerging marine toxins. Looking ahead, developing interdisciplinary cooperation, strengthening monitoring of emerging marine toxins, and exploring more novel approaches are essential to better address the risks of marine toxins posed by climate change. Altogether, the interrelationships between climate, marine ecology, and marine toxins were analyzed in this study, providing a theoretical basis for preventing and managing future health risks from marine toxins.
Superoxide dismutase (SOD) is an important antioxidant enzyme that is involved in the first line of defense against reactive oxygen species (ROS) within cells. Herein, we determined two novel CuZnSOD and MnSOD genes from the toxic marine dinoflagellate Alexandrium pacificum (designated as ApCuZnSOD and ApMnSOD) and characterized their structural features and phylogenetic affiliations. In addition, we examined the relative gene expression and ROS levels following exposure to heavy metals. ApCuZnSOD encoded 358 amino acids (aa) with two CuZnSOD-conserved domains. ApMnSOD encoded 203 aa that contained a mitochondrial-targeting signal and a MnSOD signature motif but missed an N-terminal domain. Phylogenetic trees showed that ApCuZnSOD clustered with other dinoflagellates, whereas ApMnSOD formed a clade with green algae and plants. Based on the 72-h median effective concentration (EC50), A. pacificum showed toxic responses in the order of Cu, Ni, Cr, Zn, Cd, and Pb. SOD expression levels dramatically increased after 6 h of Pb (≥6.5 times) and 48 h of Cu treatment (≥3.9 times). These results are consistent with the significant increase in ROS production in the A. pacificum exposed to Pb and Cu. These suggest that the two ApSODs are involved in the antioxidant defense system but respond differentially to individual metals.
Electrophysiology studies the electrical properties of cells and tissues including bioelectrical signals and membrane ion channel activities. As an important means to reveal ion channel related physiological functions and the underlying mechanisms, electrophysiological techniques have been widely used in studies of animals, higher plants and algae that are closely related to higher plants. However, few electrophysiological studies have been carried out in red tide organisms, especially in dinoflagellates, which is mainly due to the complex surface structure of dinoflagellate amphiesma. In this study, the surface amphiesma of Alexandrium pacificum, a typical red tide species, was removed by centrifugation, low-temperature treatment and enzymatic treatment. In all three treatments, low-temperature treatment with 4 °C for 2 h had high ecdysis rate and high fixation rate, and the treated cells were easy to puncture, so low-temperature treatment was used as a preprocessing treatment for subsequent current recording. Acquired protoplasts of A. pacificum were identified by calcofluor fluorescence and immobilized by poly-lysine. A modified “puncture” single-electrode voltage-clamp recording was first applied to dinoflagellates, and voltage-gated currents, which had the characteristics of outward K⁺ current and inward Cl⁻ current, were recorded and confirmed by ion replacement, indicating the voltage-gated currents were mixed. This method can be used as a technical basis for the electrophysiological study of dinoflagellates and provides a new perspective for the study of stress tolerance, red tide succession, and the regulation of physiological function of dinoflagellates.
