A reinvestigation of saxitoxin production and sxtA in the ‘non-toxic’Alexandrium tamarense Group V clade

Abstract

The three Alexandrium species A. tamarense, A. fundyense and A. catenella include strains that can be potent producers of the neurotoxin saxitoxin (STX) and its analogues, the causative agents of paralytic shellfish poisoning (PSP). These three species are morphologically highly similar, differing from each other only in the possession of a ventral pore, or in the ability to form chains. The appropriateness of these morphological characters for species delimitation has been extensively debated. A distinctive clade of this species complex, Group V, Tasmanian clade, is found in southern Australia, and occasionally occurs in bloom proportions. This clade has been considered non-toxic, and no PSP toxins have been found in shellfish following blooms of this species. In the present study, we report on a Tasmanian strain of A. tamarense, Group V that produces STX and possesses the gene, sxtA that is putatively involved in STX production. The toxin profile was determined and is unusual, including a high proportion of GTX5 and a small amount of STX, and differs from that of co-occurring A. catenella (Group IV). A putative bloom of A. tamarense that occurred in October 2010, and the subsequent finding of STX in Sydney Rock Oysters (Saccostrea glomerata), may suggest that some naturally occurring strains of this species could produce STX.