Toxic Microcystis aeruginosa in Lake Velencei

Lake Velencei is a shallow lake in Hungary. The first cyanobacterial bloom of Microcystis aeruginosa appeared in the lake in 1991. This cyanobacterial species was also found earlier but blooms were not recorded. The toxins of M. aeruginosa were studied in Lake Velencei in 1992. The present study deals with the toxicity of a M. aeruginosa biomass of different origin detected by intraperitoneal (ip.) mouse assay, Thamnotoxkit F(TM) microbiotest, and toxin analysis by high-performance liquid chromatography (HPLC). The biomass was collected by plankton net and the isolated strains were cultured from sediments and from bloom material. Minimal lethal doses (MLD) by ip. mouse assay ranged from 20 to 50 mg/kg(-1). Comparing the results from 1992 and 1997-1998, no change in the toxicity of M. aeruginosa was detected. According to the HPLC analysis the combination of microcystins varied in a narrow range with microcystin-LR found in each sample. The cyanobacterial blooms caused by M. aeruginosa in Lake Velencei considerably decreased, though it remained in the sediment with the same toxicity. The Thamnotoxkit F(TM) microbiotest was an alternative method for detecting the cyanotoxins. (C) 2000 by John Wiley & Sons, Inc.