Paralytic shellfish toxin production by the dinoflagellate Alexandrium pacificum (Chinhae Bay Korea) in axenic nutrient-limited chemostat cultures and nutrient-enriched batch cultures

摘要

The marine dinoflagellate Alexandrium produces paralytic shellfish poisoning (PSP) toxins in temperate coastal waters worldwide. Since the 1990s, there have been frequent outbreaks of toxic A. pacificum (formerly A. tamarense; ) algal blooms tied to anthropogenic eutrophication in Chinhae Bay (Korea). Such blooms have a detrimental effect on mariculture, more specifically on the oyster, shellfish, and fishing industries. In this study, we examined the production of PSP toxin by axenic A. pacificum HYM9704 in chemostat and batch cultures using growth conditions that differed according to dilution rate, nutrient limitations, and enrichments. More specifically, we determined how these variables affected PSP toxin level and profile. We found that phosphate (P)-limited cells in chemostat cultures produced higher levels of PSP toxins with a more diverse toxin profile than nitrogen (N)-limited cells at the highest algal growth rates. In nutrient-limited batch cultures that then received N and P enrichment, the N-enriched A. pacificum HYM9704 showed a more diverse toxin profile than the enriched P-limited cells, even though the total concentration of PSP toxins following N enrichment was lower than that in the P-enriched cultures. Based on the observation that nutrient availability strongly influenced PSP toxin profile, we suggest the following order for the biosynthesis of individual toxins: C1, C2>GTX3>GTX1>neoSTX. In summary, although a higher toxicity of axenic A. pacificum HYM9704 PSP toxin was found under phosphorus limitation, nitrogen limitation and anthropogenic enrichment could also affect the nature and magnitude of toxicity in Alexandrium blooms.