ISOLATION AND CHARACTERIZATION OF MICROCYSTINS (HEPTAPEPTIDE HEPATOTOXINS) FROM PORTUGUESE STRAINS OF MICROCYSTIS-AERUGINOSA KUTZ EMEND ELEKIN

Ten toxic strains of the freshwater cyanobacteria Microcystis aerugino sa KUTZ. emend ELEKIN were isolated from natural lakes and reservoirs of North and Central Portugal. Strains were grown in Z8 medium, cells harvested and freeze-dried prior to toxin extraction. Toxins were isol ated by reverse phase HPLC and characterized by HPLC amino acid analys is, fast atom bombardment mass spectrometry and thin layer chromatogra phy. One to four microcystins were purified from each strain and a tot al of six different toxins were isolated. MCYST-LR is the most common and the dominant microcystin in all the isolated strains. MCYST-LA, MC YST-RR and MCYST-YR are also important while, MCYST-AR and [D-Asp(3)]M CYST-LR occurred as minor components. There seems to occur a significa nt difference in average cell size between natural lake and reservoir strains together with a tendency to the preferential occurrence of MCY ST-LA in natural lakes strains and MCYST-YR in the reservoir strains.