Algicidal Characteristics of Bacillus cereus Strain PT1 Against Microcystis aeruginosa in Sulfate-Type Saline–Alkaline Environments

Biologically controlling <i>Microcystis aeruginosa</i> blooms in saline-alkaline environments remains a major challenge in aquatic ecosystem management. Here, the algicidal performance of an indigenous algicidal bacterium, <i>Bacillus cereus</i> strain PT1 isolated from a sulfate-type saline-alkaline pond, against <i>M. aeruginosa</i> was evaluated, and the underlying metabolic mechanisms were elucidated using non-targeted metabolomics. PT1 exhibited pronounced, stable algicidal activity under saline-alkaline conditions, decreasing the algal cell density from 2 × 10⁶ to 1.25 ± 0.5 × 10⁵ cells mL^-1 within 4 days at a rate of 93.75 ± 2.5% (<i>p</i> < 0.05). The above results demonstrate that strain PT1 has a significant lytic effect on <i>M. aeruginosa</i>. Non-targeted liquid chromatography-mass spectrometry analysis identified 298 PT1-induced accumulated metabolic features, and the top 30 candidates comprised organic acids and aromatic compounds, including benzoic acid, coumarin, malonic acid, and signaling-related molecules, including indoleacetaldehyde and nitroprusside. These differential metabolites were associated with algicidal-related pathways, including quorum sensing, two-component systems, ABC transporters, and tryptophan metabolism, outlining a coordinated "regulation-transport-metabolic remodeling" framework. Our findings demonstrate the potential of the indigenous algicidal strain PT1 from saline-alkali ponds to control <i>M. aeruginosa</i> blooms. They also provide an important theoretical basis and data foundation for further elucidating the molecular characteristics of algae solubilizing activity under saline-alkali conditions and developing microbial agents for preventing and controlling <i>Microcystis</i> blooms in saline-alkali ponds.