Abstract
The protein phosphatase inhibition assay was used to quantify low levels of microcystin in lake water polluted by cyanobacterial blooms of Microcystis, and toxin concentrations in cultures of 15 strains of Microcystis. This method was highly sensitive permitting measurement of microcystin in concentrations of the order of μg1-1. The concentrations of microcystin in the surface water of Lake Kasumigaura in the summer of 1995 were in the range of 0.16 to 2.7μg1-1 microcystin-LR equivalents.
On the other hand, markedly high levels of microcystin (160 to 1, 429μg1-1) were measured in the culture fluids of M. aeruginosa TAC 192-2, M. ichthyoblabe TAC 69, M. ichthyoblabe TAC 113-1, M. viridis TAC 45-1, M. viridis TAC 64 and M. viridis TAC 92. There were strains which did not produce microcystin in the culture fluid within the same species of Microcystis. Therefore, the toxin productivity in the culture fluid is not a useful criterion for discrimination of the species of Microcystis.
