Degradation of the cyanobacterial hepatotoxin microcystin by aquatic bacteria

Bacterial degradation of the cyanobacterial cyclic peptide hepatotoxin microcystin was confirmed in natural waters and by isolated laboratory strains. Degradation of 1 mg L-1 microcystin LR typically began 2-8 days after addition to surface water samples. At concentrations greater than 1 mg L-1 there was an initial slow removal of microcystin LR, rather than a distinct lag (or conditioning) phase, before rapid degradation commenced. The lag phase was absent upon re-addition of microcystin LR to the water. Both single strains and mixed bacterial cultures capable of degrading microcystin LR were isolated from surface water samples. One single strain isolated was a gram-negative rod and appeared to be a Pseudomonas sp., although standard taxonomic tests have given inconclusive results. Degradative activity was mostly intracellular and equally active against microcystin LR and RR, but not against nodularin.