Comparative studies on morphology, ITS sequence and protein profile of Alexandrium tamarense and A. catenella isolated from the China Sea

The Alexandrium tamarense species complex is a closely related cosmopolitan toxigenic group of morphology-based species, including A. tamarense, A. catenella and A. fundyense. This study investigated the morphology, internal transcribed spacer (ITS) sequence and protein profile of A. tamarense and A. catenella grown in the same culture conditions using a combination of scanning electronic microscope (SEM), molecular and proteomic approaches. The results showed that all Alexandrium strains had the plate formula of Po, 4′, 6″, 6C, 8S, 5″′, 2″″. The ventral pore, a key conventional morphological feature to discriminate A. tamarense and A. catenella, was usually present in the first apical plate of ten A. tamarense strains, however, it was found to be absent in some cells of one Alexandrium strain, ATGX01. A. tamarense and A. catenella shared an identical ITS sequence with a minor variation at intraspecific level. Protein profiles of A. catenella DH01 and A. tamarense DH01, isolated from the same region of the East China Sea, showed no significant difference, the similarity of protein profiles of the two species reached 99% with a few proteins unique to one or the other. The present results suggest that the ventral pore is not a consistent morphological feature in the Alexandrium genus, and that A. tamarense and A. catenella are conspecific and should be redesignated to one species.