Heptapeptide toxins contained in natural samples of Microcystis species

Toxins contained in Microcystis species were examined for natural samples of water bloom collected from several lakes in Japan. The toxins were identified as microcystins (cyanoginosins)‐LR,‐YR, and ‐RR. The amounts of the three toxins were estimated after adsorption to a C18 cartridge, eluted with methanol, and subjected to high performance liquid chromatography using an octa decylsilanized column. Microcystins‐RR and ‐LR were the main components of the toxins contained in natural samples of Microcystis bloom, while YR was not detected in more than half of the samples analyzed. Six samples were also examined in relation to LD 50 values and species composition of Microcystis . The highest total amount of the three toxins was obtained for the sample with the lowest LD 50 value and composed mostly of cells of M. aeruginosa . The relation between LD 50 values and total contents of the three toxins was well fitted to the formula Y = 1100 × X −1.079 , where Y is the LD 50 value and X is the total amount of the three toxins.