Identification of the toxic dinoflagellates Alexandrium catenella and A-tamarense (Dinophyceae) using DNA probes and whole-cell hybridization

Fluorescent DNA probes (cCAT-F1 and cTAM-F1) complementary to the 3' end of ribosomal RNA (rNA) internal transcribed spacer 1 sequences (ITS 1: positions 154-176) of toxic species of Alexandrium catenella (Whedon and Kofoid) Taylor and A. tamarense (Lebour) Taylor were applied to various cultures of the genus Alexandrium and several other phytoplankters using whole-cell fluorescent in situ hybridization. cCAT-F1 and cTAM-F1 reacted with targeted strains of A. catenella (catenella type) and A. tamarense (tamarense type), respectively, and did not react with isolates of A. affine (Inoue et Fukuyo) Balech, A. fraterculus (Balech) Balech, A. insuetum Balech, A. lusitanicum Balech, A. pseudogonyaulux (Biecheler) Horiguchi ex Yuki et Fukuyo comb. nov., nor isolates of Prorocentrum micans Ehrenberg, Amphidinium carterae Hulburt, Heterocapsa triquetra (Ehrenberg) Stein, Gymnodinium mikimotoi Miyake et Kominami ex Oda, Skeletonema costatum (Greville) Cleve, Heterosigma akashiwo(Hada) Hada, and Chattonella antiqua (Hada) Ono. DNase I and RNase A treatment showed that probes hybridized to ribosomal DNA, not rDNA. Probes were localized at the bottom of the U-shaped nucleus, a region that corresponds to the nucleolus. The probes are highly specific for particular strains of A. catenella and A. tamarense and are applicable for identifying these species collected from cultured and possibly natural populations.