Isolation, characterization and quantification of microcystins (heptapeptides hepatotoxins) in Microcytis aeruginosa dominated bloom of Lalla Takerkoust lake-reservoir (Morocco)

This paper presents the first data on the identification, characterization and quantification of microcystins isolated from both an extract of a cyano bacteria natural bloom, collected from a eutrophic Moroccan reservoir (Lall a Takerkoust, Marrakesh) and an isolated strain cultivated under laboratory conditions. The isolation and purification of toxins was performed by reve rse phase HPLC and then characterized by amino acid analysis and fast atom bombardment mass spectrometry (FAB-MS). Chemical characterization of the to xins from the bloom revealed variants of microcystins such as Mcyst-LR, Mcy st-RR, Mcyst-YR and [D-Asp(3)]Mcyst-LR. However, the Microcystis aeruginosa strain produced only Mcyst-RR. Using an ELISA assay the total microcystin contents of eight bloom samples collected from 1994 to 1997 ranged from 0.7 to 8.8 mug/mg of lyophilized material. The two isolated Microcystis strain s contained higher amounts of microcystins (0.65 mug/mg of dry weight) than the Pseudanabaena strains (0.021 mug/mg of dry weight). Our results show t hat the presence of cyanobacteria toxins in water used for drinking in a No rth African country may be regarded as an health hazard. These results are a contribution to the knowledge of the biogeography of toxic cyanobacteria and their toxins, namely in north African countries. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.