Detection and identification of potentially toxic cyanobacteria: Ubiquitous distribution of Microcystis aeruginosa and Cuspidothrix issatschenkoi in Japanese lakes

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We studied the frequency and composition of potentially toxic cyanobacteria in 30 samples from 25 Japanese lakes using automated rRNA intergenic spacer analysis (ARISA) and eight primer sets for nodularin, microcystin, cylindrospermopsin, anatoxin-a, and saxitoxin synthetase genes. Potential microcystin- and anatoxin-a-producers were detected in 25 and 7 samples, respectively. Cylindrospermopsin- or saxitoxin-producers were not detected. PCR and clone library analyses indicated that Microcystis was the sole microcystin-producing genus. Moreover, potential microcystin-producing Microcystis strains were detected in 25 of 26 samples which included Microcystis ARISA fragments, suggesting that toxic Microcystis is ubiquitous. Potential anatoxin-a-producers detected in the samples were estimated to be Cuspidothrix issatschenkoi (synonym: Aphanizomenon issatschenkoi) from clone library analyses of the anatoxin-a biosynthesis gene cluster and 16S–23S rDNA intergenic spacer region. Anatoxin-a-producing strains of C. issatschenkoi are known from two lakes in New Zealand and Germany. In contrast, C. issatschenkoi was the second most common toxic cyanobacteria in our study. This is the first report of potential anatoxin-a-producing C. issatschenkoi strains in Asia.