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

## TL;DR

This study investigates a marine bacterium's ability to remove lead and cadmium from soil and optimize its production of a substance useful for bioremediation.

## Contribution

The study identifies distinct mechanisms for Pb2+ and Cd2+ immobilization and optimizes fermentation for EPS production without metal stress.

## Key findings

- Cd2+ removal is linked to pH increase and likely precipitation, while Pb2+ is sequestered via EPS synthesis.
- Optimized fermentation achieved 1.081 g/L EPS without metal stress, using conditions like 45 g/L sea salt and pH 6.0.
- Strain Hao 2023 shows metal-specific resistance and potential for scalable soil remediation applications.

## Abstract

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.