Effect of a Freshwater Bacterium on Four Microcystis under Eutrophic Conditions

The effect of a freshwater bacterium Exiguobacterium sp.013 was examined on the cultures of four freshwater Microcystis which can cause cyanobacterial blooms. Four freshwater Microcystis cells and the bacterium were inoculated simultaneously, in modified BG-11 culture media, and cultured for 24 days continuously. The specific growth rate and cell densities were employed and determined in treated cultures and in controls.Additionally, dynamic changes of bacterium were investigated during the whole cultures. The results showed that the specific growth rate and maximal cell density of M. aeruginosa, M. flos-aquae and M. wesenbergii in treated cultures were significantly enhanced than that of control cultures, and daily cell densities of four Microcystis in the treated cultures were also significantly higher compared with that of control cultures. The added bacterial strain always kept dominance among the bacterial flora during the culture period. These findings implied that bacteria Exiguobacterium sp. might play a positive promoting role in forming Microcystis blooms under the eutrophication condition.