Isolation and characterization of microcystins, cyclic heptapeptide hepatotoxins from a Lake Erie strain of Microcystis aeruginosa

Cyanobacteria (blue-green, algae) dominated by Microcystis aeruginosa were detected in phytoplankton samples collected from several sites in the western basin of Lake Erie during the summer of 1996 and one site in 1995. Toxin content of the samples was measured using ELISA and found to be equivalent to as much as 1 mu g microcystin/L. Microcystins are potent liver toxins and tumor promoters produced by several genera of cyanobacteria. The Lake Erie M. aeruginosa colony strain (LE-3) was isolated and cultured to characterize chemically the specific microcystins (MCYSTs) present. Structures were assigned based on analytical high performance liquid chromatography (HPLC) retention times, amino acid analyses, and mass spectrometric data, revealing the leucine-arginine analog, microcystin-LR as the predominant product.