Biocontrol of Cladophora by Bacillus subtilis: Transcriptomic insights into algal inhibition and macrophyte restoration

The restoration of lake water quality using submerged macrophytes faces significant challenges, particularly from the explosive growth of Cladophora , which competes for resources and forms algal mats upon decay, thereby hindering restoration effectiveness. This study explores the potential of Bacillus subtilis as a biocontrol agent against Cladophora , a genus of filamentous green algae that hinders lake water quality restoration. We found that B. subtilis effectively inhibits Cladophora growth, reducing biomass and increasing superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels. It also reduced the photosynthetic efficiency of Cladophora , manifested as a decrease in Fv/Fm values and changes in photosynthetic parameters. Transcriptomic analysis revealed downregulation of key genes involved in chlorophyll biosynthesis, photosynthesis, ribosomal function, biotin metabolism, and DNA repair pathways. Importantly, applying B. subtilis powder at 2 mg/L did not negatively affect the submerged macrophyte Vallisneria denseserrulata , which grew in this treatment. This suggests B. subtilis can enhance the competitive advantage of submerged macrophytes over harmful algae, promoting effective aquatic ecological restoration. Overall, B. subtilis is positioned as a sustainable and eco-friendly alternative for managing filamentous green algal blooms and improving freshwater ecosystem health, warranting further research into its metabolic products and specific inhibitory mechanisms. • Cladophora hinders the growth of submerged macrophytes. • Bacillus subtilis rapidly destroys Cladophora cell structure. • Bacillus subtilis dysregulates gene expression in Cladophora. • Bacillus subtilis promotes submerged macrophyte growth.