Genetic polymorphism in Gymnodinium galatheanum chloroplast DNA sequences and development of a molecular detection assay

Nuclear and chloroplast-encoded small subunit ribosomal DNA sequences were obtained from several strains of the toxic dinoflagellate Gymnodinium galat heanum. Phylogenetic analyses and comparison of sequences indicate that the chloroplast sequences show a higher degree of sequence divergence than the nuclear homologue. The chloroplast sequences were chosen as targets for th e development of a 5'-3' exonuclease assay for detection of the organism. T he assay has a very high degree of specificity and has been used to screen environmental water samples from a fish farm where the presence of this din oflagellate species has previously been associated with fish kills. Various hypotheses for the derived nature of the chloroplast sequences are discuss ed, as well as what is known about the toxicity of the species.