Biocontrol potential of estuarine bacterium Pseudoalteromonas sp. S-2: algicidal activity and mechanism against Microcystis aeruginosa

Abstract

The proliferation of harmful cyanobacterial blooms, particularly Microcystis aeruginosa, poses significant threats to aquatic ecosystems and water security globally. Microbial control strategies have gained significant research interest as an environmentally sustainable and target-specific solution for Microcystis bloom management. This study investigated the algicidal activity and mechanism of Pseudoalteromonas sp. S-2, an estuarine bacterium, against M. aeruginosa. The results showed that at a concentration of 2 % (v/v), S-2 achieved 91.7 % mortality in M. aeruginosa within 96 h via an indirect mechanism. Physiological and molecular analyses revealed that S-2's cell-free supernatant induced oxidative stress, disrupted photosynthesis, carbohydrate metabolism, and protein synthesis in M. aeruginosa. Specifically, S-2 modulated antioxidant enzymes, caused membrane damage evidenced by increasing malondialdehyde accumulation and downregulating essential photosynthetic genes (psaB, psbD, and rbcL). Scanning electron microscopy (SEM) observations documented progressive morphological changes leading to cellular lysis in M. aeruginosa. Furthermore, the algicidal compounds exhibited remarkable stability across a wide range of temperatures (−80–120 °C) and pH values (4–12). Optimal environmental conditions for maximum algicidal efficacy were also identified. These findings establish Pseudoalteromonas sp. S-2 as a promising environmentally robust biocontrol agent for mitigating cyanobacterial blooms.