Biodegradation of microcystins by bacterial communities co-existing with the flagellate Monas guttula and concurrent succession of community structures

Grazing on Microcystis by the flagellate Monas guttula causes simultaneous degradation of microcystins (MCs) produced by Microcystis in culture. Although the MC-degrading bacterial strains that co-exist with M. guttula have been isolated, it is still unknown if the MC-degrading bacteria can degrade MCs within the indigenous bacterial community co-existing with M. guttula. To investigate this, we separated two indigenous bacterial communities (free-living and cell-bound) from M. guttula culture to test the ability of each community to degrade MCs. Results showed that MCs were rapidly degraded to undetectable level, and earlier MC exhaustion due to biodegradation was evident after re-spiking with MCs in both communities. These findings show that the MC-degrading bacteria are distributed over both communities, and can degrade MCs within the indigenous bacterial community co-existing with M. guttula. Denaturing gradient gel electrophoresis (DGGE) revealed differences in species diversity and structure between the two communities. Cluster analysis for DGGE patterns indicated that cell-bound community structures responded more sensitively than free-living community during degradation, and the two community structures evolved closer genetically with each other along the degradation period.