BIOTRANSFORMATION OF THE CYANOBACTERIAL HEPATOTOXIN MICROCYSTIN-LR, AS DETERMINED BY HPLC AND PROTEIN PHOSPHATASE BIOASSAY

Microcystin-LR (MCLR) is a cyclic hepatotoxin and tumor promotor produ ced by some freshwater cyanobacteria. The occurrence of microcystin-co ntaining blooms in freshwater has been implicated in animal and human poisonings worldwide. To assess the fate of MCLR in a heterotrophic mi crobial population, purified MCLR was incubated with a microbial commu nity orginating from the Edmonton wastewater treatment plant. After 10 days of aerobic incubation, a significant decrease in MCLR concentrat ion was observed. Analysis of the culture supernatant by highperforman ce liquid chromatograph, monitoring absorbance at 210 and 238 nm, sugg ested that the heptapeptide ring of MCLR and its Adda group had been m odified, respectively. The transformed product(s) of MCLR, unlike the parent toxin, did not inhibit protein phosphatase activity. There was no difference in the bacterial counts in effluent spiked with MCLR as compared with effluent without MCLR. Based on first-order kinetics, th e half-life of MCLR under our laboratory conditions ranged from 0.2 to 3.6 d.