Toxigenic Cyanobacteria and Microcystins in a Large Northern Oligotrophic Lake Onego, Russia

Toxigenic cyanobacteria and microcystins in the oligotrophic pelagic zone and mesotrophic bay of Lake Onego-the second largest lake in Europe-were found for the first time. Microscopic analysis revealed that <i>Dolichospermum lemmermannii, D. circinale</i> and <i>D. spiroides</i> dominated in bloom spots in the oligotrophic zone of the lake and <i>D. flos-aquae</i> and <i>Microcystis aeruginosa</i> OKin the eutrophic bay. The abundance of cyanobacteria in bloom spots is potentially hazardous for humans and animals. PCR-analysis showed that <i>mcyA</i> gene involved in microcystin biosynthesis was found in cyanobacteria of the genera <i>Dolichospermum</i> and <i>Microcystis</i>. Five structural variants of intracellular microcystins were detected in a trace amount using high-performance liquid chromatography-mass-spectrometry of high resolution. The most hazardous hepatotoxin, MC-LR, was found only in the eutrophic bay. In the present study, the reasons for the low cyanotoxin content in the phytoplankton dominated by <i>Dolichospermum</i> are discussed. The findings of our study make a significant contribution to the accumulation of facts which state that toxigenic cyanobacterial blooms can occur in large oligotrophic lakes.