Multifunctional Potential of Bacillus vallismortis C-305 for Cyanobacterial Bloom Suppression: Algicidal Activity, Organic Matter Transformation, and Plant Stress Mitigation.

Harmful algal blooms (HABs), particularly those caused by Microcystis aeruginosa, pose severe threats to aquatic ecosystems and agricultural irrigation safety. Biological control using algicidal bacteria offers an environmentally sustainable alternative to conventional mitigation strategies. In this study, a highly efficient algicidal bacterium, Bacillus vallismortis strain C-305, was isolated and evaluated for its inhibitory activity against M. aeruginosa. Strain C-305 exhibited strong algicidal activity and was accompanied by significant alterations in algal cellular integrity and extracellular organic matter (EOM) fluorescence characteristics. Metabolite analysis identified extracellular compounds, including erucamide, with demonstrated inhibitory activity against M. aeruginosa. Furthermore, immobilization of C-305 in sugarcane bagasse-alginate beads improved its applicability in a rice cultivation system exposed to algal-contaminated water, resulting in enhanced plant growth performance and alleviated oxidative stress responses compared with untreated conditions. These findings demonstrate the potential of B. vallismortis C-305 as a multifunctional biological agent, integrating algicidal activity, organic matter transformation, and plant-associated benefits within a microbial-based strategy for HAB management.