Algicidal characteristics and mechanism of a newly identified bacterium Pseudomonas fulva EH5 against Microcystis aeruginosa.

Microcystis aeruginosa (M. aeruginosa) blooms threaten aquatic ecosystems and drinking water safety. Algicidal bacteria offer an eco-friendly approach to control Microcystis blooms, yet few strains can simultaneously inhibit algae growth and reduce microcystin production. Herein, we isolated an efficient algicidal bacterium Pseudomonas fulva EH5 and explored its inhibitory effects and underlying mechanisms against M. aeruginosa. Strain EH5 exerted prominent algicidal activity mainly via secreted active substances, with a 97.33% inhibition rate at a 4% inoculation ratio on day 5. EH5 displayed high algicidal activity against harmful cyanobacteria, while exerting limited adverse impacts on non-target algae and zebrafish. Rather than causing widespread lysis of M. aeruginosa cells, EH5 inflicted severe damage to intracellular thylakoid structures. In addition, EH5 markedly repressed the expression of microcystin synthesis genes and reduced microcystin contents. The algicidal substances of EH5 were presumed to be intracellular-targeting polypeptides with strong acid‑base stability. The algicidal effect of EH5 against M. aeruginosa might be primarily attributed to its impairment of the photosynthetic system. Meanwhile, mild oxidative stress induced by EH5 might serve as a synergistic factor to accelerate algal suppression. Collectively, strain EH5 is a promising candidate for the ecological control of Microcystis blooms and microcystin pollution.