Variations in physiological responses among eight strains of toxin-producing dinoflagellate Alexandrium pacificum and the diversity in the paralytic shellfish toxin biosynthesis gene (sxtA4)

Abstract

Numerous studies have been conducted on the mechanism of paralytic shellfish toxin production in the genus Alexandrium, but many aspects still remain a mystery. This species exhibits substantial intraspecific variations in toxin composition and production levels. However, the precise underlying causes for this phenomenon have yet to be elucidated. Therefore, in this study, we aimed to illuminate the causes of such differential toxin production among eight strains of A. pacificum. We compared and analyzed the differences in toxin production (both quantity and composition) among these strains under four different temperatures (15，20，25 and 30 °C). Additionally, to understand its toxin production differences, we conducted an analysis of the nucleotide sequence of the paralytic shellfish toxin biosynthesis gene (sxtA4). Consequently, under unfavorable growth conditions for each strain. A distinct disparity in PST compositions was evident between the two strains, KM2 and KM5, with strain KM5 exhibiting the greatest diversity of PST components whereas strain KM2 exhibiting the simplest diversity. To examine whether or not this difference might be derived from intraspecific genetic diversity between the strains, we investigated the sequences of the sxtA4 gene which is a core initiating gene for PST production using a cloning method. Interestingly, the sxtA4 gene in strain KM5 had more single nucleotide polymorphisms (88 SNPs/615 bp) than that in strain KM2 (54 SNPs/615 bp). Given these findings, the number of SNPs may exhibit a positive correlation with the level of PST diversity in A. pacificum.