Isolation and characterization of microcystins from a River Nile strain ofOscillatoria tenuis Agardh ex Gomont

The River Nile is the major source of drinking water in Egypt, however, inc reased eutrophication due to agricultural, municipal and industrial runoff has contributed to the growth of toxin producing cyanobacteria. This study describes the isolation and characterization of microcystins (MCYSTs), cycl ic heptapeptide hepatotoxins, From a rare strain of Oscillatoria tenuis. is olated from the River Nile at Sohag province in July 1995. The MCYST concen tration of laboratory-cultured O. tenuis strain E6 was found to be 0.3 mg/g freeze-dried weight determined by enzyme-linked immunosorbent assay (ELISA ). Two microcystins, 1 and 2, were isolated from lyophilized cells using so lid phase extraction and reversed-phase high performance liquid chromatogra phy (HPLC). Structures were assigned based upon their amino acid analyses, electrospray ionization mass spectrometry (ESIMS, ESIMS-CID-MS), high resol ution fast atom bombardment mass spectrometry, and nuclear magnetic resonan ce data (H-1 and H-1 COSY NMR). Toxin 1 was identified as MCYST-LR, and tox in 2, a new MCYST, as MCYST-LHArg ([L-homoarginine(4)]). Previous studies i ndicate that Oscillatoria agardhii strains produce demethylated MCYSTs (con taining D-Asp and/or dehydroalanine). This is the first report of a toxic O . tenuis, strain E6, one which produces a fully methylated MCYST, MCYST-LR and a new L-homoarginine containing MCYST, MCYST-LHArg . (C) 2000 Elsevier Science Ltd. All rights reserved.