Toxin Profile of Two Gymnodinium catenatum Strains from Iberian Coastal Waters

Effect of temperature, salinity and nutrients on the growth and toxin content of the dinoflagellate Gymnodinium catenatum from the southwestern Mediterranean

The dinoflagellate Gymnodinium catenatum is considered the primary cause of recurrent paralytic shellfish toxins (PSTs) in shellfish on the Moroccan Mediterranean coasts. The impacts of key environmental factors on the growth, cell yield, cell size and PST content of G. catenatum were determined. Results indicated that increasing salinity from 32 to 39 and nitrate concentrations from 441 μM to 1764 μM did not significantly (ANOVA, P-value >0.63) modify the growth rate of the studied species. Gymnodinium catenatum exhibited the highest growth rate at 24 °C. Cells arrested their division at 15 °C and at ammonium concentration above 441 μM, suggesting that this nitrogen form is toxic for G. catenatum. Furthermore, G. catenatum was unable to assimilate urea as a nitrogen source. In G. catenatum cells, eight analogues of saxitoxin were detected, belonging to the N-sulfocarbamoyl (C1-4, B1 and B2) and decarbamoyl (dc-GTX2/3) toxins. C-toxins contributed 92 % to 98 % of the molar composition of the PSTs. During the exponential growth, C2 tended to dominate, while C3 prevailed during the stationary phase. Toxin content per cell (ranging from 5.5 pg STXeq.cell-1 to 22.4 pg STXeq.cell-1) increased during the stationary growth phase. Cell toxin content increased with the concentrations of nitrate, ranging from 12.1 pg STXeq.cell-1 at 441 μM to 22.4 pg STXeq.cell-1 at 1764 μM during the stationary growth phase. The toxin content of G. catenatum showed the highest values measured at the highest tested temperatures, especially during the stationary phase, where toxicity reached 17.8 pg STXeq.cell-1 and 16.4 pg STXeq.cell-1 at 24 °C and 29 °C, respectively. The results can help understand the fluctuations in the growth and PST content of G. catenatum in its habitat in response to changing environmental variables in the Mediterranean Sea when exposed to increases in warming pressure and eutrophication.

Can exposure to Gymnodinium catenatum toxic blooms influence the impacts induced by Neodymium in Mytilus galloprovincialis mussels? What doesn't kill can make them stronger?

The presence in marine shellfish of toxins and pollutants like rare earth elements (REEs) poses a major threat to human well-being, coastal ecosystems, and marine life. Among the REEs, neodymium (Nd) stands out as a widely utilized element and is projected to be among the top five critical elements by 2025. Gymnodinum catenatum is a phytoplankton species commonly associated with the contamination of bivalves with paralytic shellfish toxins. This study evaluated the biological effects of Nd on the mussel species Mytilus galloprovincialis when exposed to G. catenatum cells for fourteen days, followed by a recovery period in uncontaminated seawater for another fourteen days. After co-exposure, mussels showed similar toxin accumulation in the Nd and G. catenatum treatment in comparison with the G. catenatum treatment alone. Increased metabolism and enzymatic defenses were observed in organisms exposed to G. catenatum cells, while Nd inhibited enzyme activity and caused cellular damage. Overall, this study revealed that the combined presence of G. catenatum cells and Nd, produced positive synergistic effects on M. galloprovincialis biochemical responses compared to G. catenatum alone, indicating that organisms' performance may be significantly modulated by the presence of multiple co-occurring stressors, such those related to chemical pollution and harmful algal blooms. ENVIRONMENTAL IMPLICATIONS: Neodymium (Nd) is widely used in green technologies like wind turbines, and this element's potential threats to aquatic environments are almost unknown, especially when co-occurring with other environmental factors such as blooms of toxic algae. This study revealed the cellular impacts induced by Nd in the bioindicator species Mytilus galloprovincialis but further demonstrated that the combination of both stressors can generate a positive defense response in mussels. The present findings also demonstrated that the impacts caused by Nd lasted even after a recovery period while a previous exposure to the toxins generated a faster biochemical improvement by the mussels.

Cation-Exchange Resin Applied to Paralytic Shellfish Toxins Depuration from Bivalves Exposed to Gymnodinium catenatum

The accumulation of marine biotoxins in shellfish and their consumption causes serious food safety problems, threatening human health and compromising the availability of protein-based food. It is thus urgent to develop methodologies for the detoxification of live bivalves, avoiding their economic and nutritional devaluation. In this context, we tested an adsorption mechanism of paralytic shellfish toxins (PST) based on a cation-exchange resin. The first studies using cultures of Gymnodinium catenatum (natural producers of PST) showed a decrease of about 80% in overall toxicity after 48 h. Interestingly, we found that the toxins are adsorbed differently, with toxins' structural features playing a part in the adsorption capacity via steric hindrance, electronic effects, or the extent of positive charge density (e.g., dcSTX). The positive effect of the resin in accelerating PST clearance from live mussels (Mytilus edulis) is not evident when compared to resin-free clearance; nevertheless, relevant information could be gathered that will facilitate further in vivo studies. Several factors appear to be at play, namely the competition of natural substances (e.g., salts, organic matter) for the same binding sites, the blocking of pores due to interactions between molecules, and/or difficulties in resin absorption by mussels. Additionally, the present work revealed the ability of mussels to neutralize pH and proposes bioconversion reactions among the PST molecules.