Variation of Microcystin Content of Cyanobacterial Blooms and Isolated Strains in Lake Grand-Lieu (France)

Abstract

Cyanobacterial blooms were sampled at five locations in Lake Grand-Lieu on seven different occasions during May–October 1994. Strains of Microcystis aeruginosa and Anabaena circinalis were isolated from the samples. Microcystins were detected in freeze-dried field samples and the isolated strains by HPLC. The toxins were present in the blooms sampled between June and October. The microcystin content in the blooms varied with site and time, from undetectable concentrations to 0.23 mg g⁻¹. The highest concentrations of microcystin were found in blooms sampled in September. Microcystin-LR and microcystins with retention times close to the retention time of [Dha⁷]microcystin-RR (probably varieties of microcystin-RR) were found in the field samples. Sixteen of the 98 isolated M. aeruginosa strains and 2 of the 24 A. circinalis strains produced microcystins. The total amount of microcystins varied from undetectable concentrations to 5.06 mg g⁻¹ in the M. aeruginosa isolates, and from undetectable concentrations to 1.86 mg g⁻¹ in the A. circinalis strains. Microcystin-LR was the main toxin found in strains of M. aeruginosa, but was not present in strains of A. circinalis. Both microcystin-producing strains and strains that did not produce microcystin coexisted in the bloom samples.