Paucibacter Aquatile DH15 Kills Microcystis Aeruginosa Via Both Direct and Indirect Attacks

The excessive proliferation of Microcystis aeruginosa can lead to ecological damage, economic losses, and threaten animal and human health. For controlling Microcystis blooms, microorganism-based methods have attracted much attention from researchers because of their eco-friendliness and species-specificity. Herein, we first found that a Paucibacter strain exhibits algicidal activity against M. aeruginosa and microcystin degradation capability. Paucibacter aquatile strain DH15 was isolated from freshwater during a natural Microcystis bloom. We demonstrated that the algicidal activity of DH15 against M. aeruginosa can be mediated by physical attachment and indirect attack: (1) Both washed cells and cell-free supernatant could kill M. aeruginosa efficiently; (2) M. aeruginosa cells that did not directly contact DH15 cells were not lysed; (3) Treatment with DH15 cell-free supernatants caused oxidative stress, altered the fatty acid profile, and damaged photosynthetic system, carbohydrate, and protein metabolism in M. aeruginosa . The combination of direct and indirect attacks supported that strain DH15 exerts high algicidal activity against M. aeruginosa . The expression of most key genes responsible for photosynthesis, antioxidant activity, microcystin synthesis, and other metabolic pathways in M. aeruginosa was downregulated. Strain DH15, with its microcystin degradation capacity, can overcome the trade-off between controlling Microcystis blooms and increasing microcystin concentration. Our findings suggest that strain DH15 possesses great potential to control outbreaks of Microcystis blooms.