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

Biologically controlling Microcystis aeruginosa blooms in saline–alkaline environments remains a major challenge in aquatic ecosystem management. Here, the algicidal performance of an indigenous algicidal bacterium, Bacillus cereus strain PT1 isolated from a sulfate-type saline–alkaline pond, against M. aeruginosa 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% (p < 0.05). The above results demonstrate that strain PT1 has a significant lytic effect on M. aeruginosa. 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 M. aeruginosa 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 Microcystis blooms in saline–alkali ponds.