Abstract：To investigate the inhibition of Bacillus subtilis against Microcystis aeruginosa, the bacterium-free filtrate of B. subtilis culture from different growth periods (delayed, log, stable and decline phase) were used to study its inhibition and mode of action against M. aeruginosa. The MDA, SOD activity and the photosynthetic pigments content in M. aeruginosa were measured. The results showed that the inhibition of M. aeruginosa by the B. subtilis filtrate was greater in log phase, stable phase and decline phase than that in delayed phase with removing efficiency of 81.19%, 91.41% and 91.82%, respectively on day 8. The chlorophyll a contents of M. aeruginosa in treated groups were significantly lower than that in the control group. The MDA contents increased obviously in treated group and the SOD activity increased first and then decreased when M. aeruginosa was cultured in the filtrate-containing medium. Carotenoids were not affected as much as chlorophyll a. Results showed that B. subtilis inhibited the growth of the algae by secreting extracellular substances. And these substances were highly thermal-stable. It was speculate that the substances can hinder the photosynthesis by destroying the photosynthetic pigments and increase the membrane lipid peroxidation by inhibiting the SOD activity at the same time, resulting in inhibition of M. aeruginosa.
