Biocompatibility of Alexandrium minutum in the growth and paralytic shellfish toxins production under five cultivation methods

Novel insights into toxin changes associated with the growth of Alexandrium pacificum: Revealing active toxin-secretion ability and toxin cell quota variation

Paralytic shellfish toxins (PSTs) are widely distributed globally and are produced by Alexandrium pacificum in marine system. However, the characteristics of toxins producing and secreting associated with growth phases are still unclear, especially whether A. pacificum has the ability to actively secrete PSTs is controversial. In this study, variation characteristics of intracellular and extracellular PSTs contents associated with A. pacificum growth phases were investigated thoroughly. The results showed that intracellular and extracellular PSTs contents increased sharply during the exponential phase. But during the stationary phase, the intracellular PSTs content increased by only 26 %, and the extracellular PSTs content did not increase significantly. Since the increase in extracellular PSTs content mainly occurred at the exponential phase, when most cells were living, we speculated that active PSTs secretion of living cells might be an important production pathway of extracellular toxins besides leakage from dead cells. Furthermore, toxin cell quota variation associated with the growth phase was analysed. In the exponential phase, the toxin cell quota first increased and then decreased, with a maximum of 19.02 ± 1.80 fmol/cell at 6 d. However, after entering the stationary phase, this value slowly increased again, suggesting that vigilance should be raised for the plateau of Alexandrium blooms. In addition, cells in the exponential phase mainly produced O-sulfated components such as GTX1&4, cells in the stationary phase mainly produced O-sulfate-free components such as GTX5. In this study, the toxigenic rules of A. pacificum were comprehensively uncovered, which provided theoretical guidance for the prevention and mitigation of A. pacificum blooms.

Rising CO2 will increase toxicity of marine dinoflagellate Alexandrium minutum

Ocean acidification caused by increasing emission of carbon dioxide (CO₂) is expected to have profound impacts on marine ecological processes, including the formation and evolution of harmful algal blooms (HABs). We designed a set of experiments in the laboratory to examine the effects of increasing CO₂ on the growth and toxicity of a toxic dinoflagellate Alexandrium minutum producing paralytic shellfish toxins (PSTs). It was found that high levels of CO₂ (800 and 1200 ppm) significantly promoted the growth of A. minutum compared to the group (400 ppm) representing the current CO₂ level. The total yields of PSTs by A. minutum, including both intracellular and extracellular toxins, were significantly enhanced, probably due to the induction of core enzyme activity and key amino acids synthesis for PST production. More interestingly, high level of CO₂ promoted the transformation from gonyautoxin2&3 to gonyautoxin1&4 and depressed the release of PSTs from inside to outside of the cells. All these processes collectively led to an apparent increase of A. minutum toxicity. Our study demonstrated that rising CO₂ would increase the risk of toxic A. minutum based on the comprehensive analyses of different processes including algal growth and toxin synthesis, transformation and release.

Effect of carboxymethyl chitosan on the detoxification and biotransformation of paralytic shellfish toxins in oyster Ostrea rivularis

Economic bivalve ingested toxic algae causes frequent human poisoning events. To explore new compounds that can accelerate the depuration of toxins in shellfish, we investigated the detoxification of the paralytic shellfish toxins (PSTs) and the biotransformation pathway of PSTs during detoxification by the application of three treatments to a toxic bloom, Alexandrium minutum (A. minutum). The detoxification effect of Platymonas subcordiformis (PS) mixed with carboxymethyl chitosan (CMC) group is significantly better than the starving group in each oyster tissues. The toxicity of viscera which occupied 78.95% of total toxicity reduced to 155 MU/100g after 13 days' depuration experiment. And adding CMC could significantly achieve rapid detoxification and effectively reduce the STX to 0.07 μmol/100 g in viscera. Meanwhile, PSTs underwent biotransformation during the depuration process, which mainly manifested as GTX1/4→GTX2/3→STX, GTX2→dcGTX2. This study explored a new strategy for toxin depuration in shellfish.