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

Ten toxic strains of the freshwater cyanobacteria Microcystis aeruginosa 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 isolated by reverse phase HPLC and characterized by HPLC amino acid analysis, fast atom bombardment mass spectrometry and thin layer chromatography. One to four microcystins were purified from each strain and a total of six different toxins were isolated. MCYST-LR is the most common and the dominant microcystin in all the isolated strains. MCYST-LA, MCYST-RR and MCYST-YR are also important while, MCYST-AR and [D-Asp(3)]MCYST-LR occurred as minor components. There seems to occur a significant difference in average cell size between natural lake and reservoir strains together with a tendency to the preferential occurrence of MCYST-LA in natural lakes strains and MCYST-YR in the reservoir strains.