Inhibiting Effects Of Bacillus Subtilis On Microcystis Aeruginosa

Cyanobacterial blooms caused by eutrophication have resulted in severe destruction of water ecosystem, and even threat to the human health. It is critical to find effective measures to control cyanobacterial blooms. The fundamental cause of the bloom is environment imbalance in water body and use biological means to solve the blooms problem will be safe and effective from the perspective of ecological balance. In recent years, these are increasing reports of algicidal bacteria and Bacillus has attracted more and more attention as a hotspot to address the environmental problems caused by cyanobacterial blooms.Bacillus subtilis is a non-lethal bacterium that widely exists in the nature. And it is a kind of probiotics commonly used in aquaculture. It has not been reported for use in algae control. Therefore, this study was conducted to investigate the inhibitory effect of B. subtilis on the major bloom species Microcystis aeruginosa for developing strategies to control cyanobacterial bloom. The results are summarized as follows:1. The asepticized research of M. aeruginosaM. aeruginosa is often accompanied by epiphytic bacteria, which affect the exploration of its interaction with algicidal bacteria. Therefore, obtaining M. aeruginosa free of bacteria is particularly critical. We investigated the feasibility to treat M. aeruginosa with antibiotics to remove bacteria. The results showed that joint treatment of the algal cells at 107cells/m L with 5mg/L of neomycin and gentamicin sulfate for 24 h, can remove epiphytic bacteria completely, and result in isolation of bacterium-free M. aeruginosa strains.2.Effects of B. subtilis on the growth of M. aeruginosaTo investigate the inhibition of M. aeruginosa by B. subtilis, bacterium-free filtrates 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 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. Our results showed that B. subtilis inhibited the growth of the algae by secreting extracellular substances. And these substances were highly thermal-stable.3. Effects of B. subtilis on the physiological characteristics of M. aeruginosaTo investigate the inhibition of B. subtilis against M. aeruginosa, MDA and SOD activity, soluble protein and the photosynthetic pigments content in M. aeruginosa were measured. The results showed that 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. The soluble protein content was higher and then lower as compared with the control group. Carotenoids were not affected as much as chlorophyll a. We speculate that the substances can hinder the photosynthesis by destroying the photosynthetic pigments and impeding the protein synthesis to inhibit the growth of the algae. On the other hand, it increased the membrane lipid peroxidation by inhibiting the SOD activity at the same time, resulting in inhibition of M. aeruginosa.In summary, B. subtilis is inhibitory to M. aeruginosa, and is an ideal species of algae bloom control. The results are instrumental to its large-scale production and application.