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

Abstract

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 Dolichospermum lemmermannii, D. circinale and D. spiroides dominated in bloom spots in the oligotrophic zone of the lake and D. flos-aquae and Microcystis aeruginosa OKin the eutrophic bay. The abundance of cyanobacteria in bloom spots is potentially hazardous for humans and animals. PCR-analysis showed that mcyA gene involved in microcystin biosynthesis was found in cyanobacteria of the genera Dolichospermum and Microcystis. 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 Dolichospermum 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.

Keywords: Lake Onego; cyanobacteria; microcystins; toxigenic species; water bloom.

Figure 1

Extracted ion chromatogram of high resolution (mass accuracy within 5 ppm) for MC congeners detected in phytoplankton samples of Lake Onego: standard mix solution, concentration 50 ng mL⁻¹ (A), sample K_50 (B), sample S_3 (C) (from top to bottom): m/z 512.78235 ([M+2H]²⁺ [D-Asp³]MC-RR); m/z 519.79077 ([M+2H]²⁺ MC-RR); m/z 981.54095 ([M+H]⁺ [D-Asp³]MC-LR); m/z 995.55658 ([M+H]⁺ MC-LR); m/z 1045.53589 ([M+H]⁺ MC-YR).

Figure 2

MS2 spectra of the MC congeners identified in the extract of sample K_50: [D-Asp³]MC-RR) (A); [D-Asp³]MC-LR) (B); MC-RR (C); MC-LR (D); MC-YR (E).

Figure 3

Example of extracted ion high-resolution chromatogram (mass accuracy within 5 ppm) of phytoplankton extract (sample S_3): phenylalanine (A), anatoxin-a (B).

Figure 4

Location of sampling stations. Lake Onego, July 2022.