Development of molecular identification method for genus Alexandrium (Dinophyceae) using whole-cell FISH

We have developed a method to identify species in the genus Alexandrium using whole-cell fluorescent in situ hybridization with FITC-labeled oligonucleotide probes that target large subunit ribosomal rRNA molecules. The probes were designed based on the sequence of the rDNA D1-D2 region of Alexandrium species. DNA probes specific for toxic A. tamarense and A. catenella and nontoxic A. affine, A. fraterculus, A. insuetum, and A. pseudogonyaulax, respectively, were applied to vegetative cells of all above Alexandrium species to test the sensitivity of the probes. Each DNA probe hybridized specifically with vegetative cells of the corresponding Alexandrium species and showed no cross-reactivity to noncorresponding Alexandrium species. In addition, no cross-reactivity of the probes was observed in experiments using concentrated natural seawater samples. The TAMAD2 probe, which is highly specific to A. tamarense, a common toxic species in Korean coastal waters, provides a simple and reliable molecular tool for identification of toxic Alexandrium species.