RELEASE AND DEGRADATION OF MICROCYSTIN FOLLOWING ALGICIDE TREATMENT OF A MICROCYSTIS-AERUGINOSA BLOOM IN A RECREATIONAL LAKE, AS DETERMINEDBY HPLC AND PROTEIN PHOSPHATASE INHIBITION ASSAY

Algicide treatment of an hepatotoxic Microcystis aeruginosa Kuetzing e mend. Elenkin bloom on Lake Centenary caused cell lysis and the releas e of microcystin into the surrounding water. Where M. aeruginosa was c onfined to accumulations along the leeward shore of the lake, dissolve d microcystin was detected for only 24 hours after spraying. It was pr esumed that the toxin was rapidly diluted by uncontaminated water from the main body of the lake. At an enclosed site in the south-west corn er of the lake, microcystin persisted at high levels (1300-1800 mu gl( -1)) for 9 days before degradation commenced. Microcystin degradation kinetics following this 9 day lag phase were bi-phasic with a rapid ph ase lasting 3 days (90-95% loss), and a slower phase which continued u ntil a flash flood on day 21. HPLC analysis and protein phosphatase as say revealed the same overall trend of microcystin release, persistenc e and then degradation. However, there was a rapid increase in protein phosphatase inhibition from day 5 to day 9 before degradation commenc ed. These results suggest that the initial bacterial transformation of microcystin resulted in a product more inhibitory to protein phosphat ase than the parent toxin.