Hepatotoxic cyanobacteria in the shallow lake Müggelsee

Abstract

Since 1996 we have studied the occurrence of cyanobacterial hepatotoxins, microcystins (Mcyst), in the shallow lake Müggelsee. Intracellular (cell-bound) Mcyst's were detectable from late summer to autumn in 2 years, and maximum concentrations of about 3 μg/l of total cell-bound Mcyst were measured. The concentration of Mcyst's was correlated to the biovolume of Microcystissp. (R ²=0.560 in 1996 and R ²=0.483 in 1997; P < 0.001). Between years, the ratio of Mcyst'ss per biovolume of Microcystisdiffered significantly (P < 0,001; 0.913 μg/mm³in 1996 and 0.171 μg/mm³in 1997). The ratio of the detected Mcyst variants, Mcyst-LR and Mcyst-RR, was constant in all samples with Mcyst-LR:Mcyst-RR≈1:2.9. One out of 22 strains of Microcystissp. we isolated in 1997 contained Mcyst-LR and Mcyst-RR at a ratio of Mcyst-LR:Mcyst-RR=1:1.6. The Mcyst'ss found in lake samples were likely to have been produced by a number of a few strains that were present in the lake for extended periods of time in both years.