Characteristics of Biodegradation of Cyanobacterial Toxin Microcystin LR in Environmental Water Under the River Die-away Test.

Abstract

The biodegradability of microcystins produced by water-bloom was examined using the river die-away test. Although microcystin LR was not degraded during the first eight days after starting the test, after the eighth day, it began to be degraded rapidly, suggesting that microcystin LR was degraded by inductive metabolism and specific biodegradation. The activity of specific degradation of microcystin LR in the samples from a pond in which water-bloom was occurring was higher than from a pond with no water-bloom. Furthermore, the activity of specific degradation of microcystin LR in the samples taken during the water-bloom season (July 2001) was higher than on no water-bloom season (June 2001) . These results show that the bacteria that can degrade microcystin LR act accompanying the occurrence of water-bloom. Also, under the alkaline condition, microcystin LR was not degraded in the sample from the pond without water-bloom, but was degraded rapidly in the sample from the pond with water-bloom. We suggest that alkaliphilic or tolerant alkaline bacteria are strongly involved in the degradation of microcystin LR in the pond with water-bloom. We concluded that the fate of microcystin in the environment depend on specific bacteria which could adapt to two requirements, specific degradation metabolism for microcystin and tolerance to alkaline environment.