Isolation and characterization of a variety of microcystins from seven strains of the cyanobacterial genus Anabaena

Hepatotoxins (microcystins) from seven freshwater Anabaena strains originating from three different Finnish lakes and one lake in Norway were isolated by high-performance liquid chromatography and characterized by amino acid analysis and fast atom bombardment mass spectrometry. All strains produced three to seven different microcystins. A total of 17 different compounds were isolated, of which 8 were known microcystins. The known compounds identified from six strains were MCYST (microcystin)-LR, [D- Asp³]MCYST-LR, [Dha⁷]MCYST-LR, [D-Asp³,Dha⁷]MCYST-LR, MCYST-RR, [D- Asp³]MCYST-RR, [Dha⁷]MCYST-RR, and [D-Asp³,Dha⁷]MCYST-RR. With the exception of MCYST-LR and [D-Asp³]MCYST-LR, this is the first time that isolation of these toxins from Anabaena strains has been reported. Three of the strains produced one to three toxins as minor components which could not be identified. Anabaena sp. strain 66 produced four unidentified toxins. The other Anabaena strains always contained both MCYST-LR and MCYST-RR and/or their demethyl variants. Quantitative differences between toxins within and between strains were detected; at times MCYST-LR and at other times MCYST-RR or demethyl derivatives thereof were the most abundant toxins found in a strain.