Abstract
In this study, we investigated the seasonal changes in the concentration of microcystins by HPLC, the composition of cyanobacteria based on the16S rRNA gene, and the presence of toxic Microcystis sp. by quantitative PCR in the surface water of Lake Hachiro, Akita prefecture, Japan. Moreover, the unialgal cultures of 8 strains of Microcystis sp., Anabaena sp., and Pseudoanabaena sp. were isolated from algal bloom. The concentration of chlorophyll a increased and algal bloom occurred when the water temperature exceeded 25°C in Lake Hachiro. The concentrations of microcystins increased from August 2008, probably because of the growth of toxic Microcysis sp., which was determined by quantitative PCR of the mcyB gene. Furthermore, the mcyA gene was also detected from a unialgal culture of Microcystis sp., and it was confirmed that some Microcysts sp. strains in Lake Hachiro was toxic. The results of this study were suggested that the change in concentration of microcystins was related to the ratio of toxic Microcystis sp. equivalents to total Microcystis sp. equivalents in Lake Hachiro.
