Differential Immobilization of Pb2+ and Cd2+ by Marine Bacillus velezensis Hao 2023: Mechanisms and Fermentation Optimization for Enhanced Exopolysaccharide Production

Soil contamination with lead (Pb) and cadmium (Cd) poses a severe threat to agricultural safety. This study explored the marine bacterium Bacillus velezensis Hao 2023 for bioremediation potential and EPS yield enhancement. Soil filtrate tests under metal stress revealed high tolerance to Pb2+ (250 mg/L) and Cd2+ (2.5 mg/L), with distinct mechanisms: Cd2+ removal was strongly correlated with significant pH increase (up to 8.10), suggesting that immobilization likely occurred through precipitation, while Pb2+ was sequestered via EPS synthesis, achieving a yield of 1.62 g/L under stress. To decouple production from metal stress, fermentation was optimized using single-factor and response surface methodology. Key conditions (sucrose, ammonium sulfate, 45 g/L sea salt, 35 °C, pH 6.0, 8% inoculum, 150 rpm) achieved 1.081 g/L EPS under metal-free conditions. These results demonstrate strain Hao 2023’s metal-specific resistance and provide a scalable process for soil remediation agent development.