Abstract

Eutrophication is still a severe global problem, and cyanobacterial microcystins (MCs) have been detected in sea areas such as harbors and coastal regions in addition to freshwater areas. Therefore, it is necessary to clarify the fate of MCs in sea areas. In Japan, Isahaya-Shin-ike-Pond, a freshwater area divided by the dike from Isahaya-bay, Nagasaki-prefecture, has eutrophicated, and cyanobacterial blooms have occurred sometimes. Water in Isahaya-Shin-ike-Pond is regularly discharged to Isahaya-bay to control the water levels in Isahaya-Shin-ike-Pond. Some researchers in Japan detected MCs from the sediment sample of Isahaya-bay; thus, MCs discharged from Isahaya-Shin-ike-Pond could be threatening the environment in Isahaya-bay. In this regard, some bacterial consortiums were isolated from Isahaya-Shin-ike-Pond and Isahaya-bay, which might degrade Microcystin-LR (MC-LR), the highly toxic representative MCs. In this report, we screened and determined the MCs degradation activity in these bacterial consortiums. As a result, we found that all bacterial consortiums degrade MC-LR. Furthermore, the HPLC chromatogram had the peak of substance-like intermediate of MC-LR decomposition. Consortium collected from approximately 4,900 m offshore from the dike degraded 97% of MC-LR. Although the bacterial communities in these consortiums differed, Bacillus sp. was in both consortiums collected from Isahaya-Shin-ike-Pond and Isahaya-bay. Because some strain of Bacillus sp. has the potential for MCs degradation, it might play an essential role in these bacterial consortiums. These results indicate that the bacteria degrade MCs even though MCs are discharged from the Isahaya-Shin-ike-Pond to Isahaya-bay.

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