PRELIMINARY FINDINGS ON GENE EXPRESSION STUDY OF SXTA1 IN ALEXANDRIUM MINUTUM

The genus Alexandrium is known for the production of potent neurotoxins affecting health of marine organisms, as well as of human seafood consumers via paralytic shellfish poisoning (PSP). Recently, Alexandrium spp. population genetic and gene expression studies have received considerable attention, in the attempt to identify genes involved in PSP toxin production. The aim of this work was to investigate the relationship between toxin content and expression level of gene sxtA1 in order to provide a new tool for predicting toxins??? presence in environmental samples. Indeed, this gene encodes for a poliketide synthase, the enzyme responsible for initiating the synthesis of saxitoxins. In our study, chemical analyses on PSP toxin composition and content in different Mediterranean A. minutum isolates confirmed that A. minutum was able to synthesize only the saxitoxin derivatives GTX1 and GTX4. Average cellular toxin content in standard condition varied considerably among different strains, ranging from 3.4 fmol/cell to traces per cell. The quantification of intracellular sxtA1 mRNA was very variable with significant differences between the phases of growth, culture conditions or strains. Moreover, the sxtA1 expression decreased during stationary phases and significant differences in strains that were grown in limitation of phosphorus or nitrogen were also observed compared to the standard culture conditions. Unexpectedly, the amount of sxtA1 messengers were not correlated with the amount of intracellular toxins in the strains analyzed suggesting that the production of toxins may be regulated probably by post-transcriptional mechanisms and/or by the concerted actions of alternative genes belonging to PSP toxin biosynthesis gene cluster.