Enhancing cadmium biosorption capacity in E. coli through heterologous expression of metal-chelating proteins: Insights into bioremediation potential and mechanisms

Cadmium (Cd) is a biologically non-essential and toxic heavy metal that enters the environment through natural emissions or anthropogenic activities, posing threats to human health. The efficient expression of metal-chelating proteins (MCP) in microorganisms can enhance microbial remediation of Cd. In this study, a heterologous expression system (GEM01) of MCP encoded by the mcp gene in E. coli was constructed, and the adsorption effect and potential mechanism on Cd were explored. The results indicated that Cd²⁺ significantly enhanced the abundance of mcp gene in GEM01, thus increasing the Cd²⁺ biosorption capacity (8.09 mg/g, 2.32 times higher than the control). The retention of Cd²⁺ during the autolysis of GEM01 was 87.87%. Fluorescence spectroscopy and molecular dynamics simulations demonstrated that there was a strong interaction between Cd²⁺ and MCP. FT-IR demonstrated that some functional groups (e.g., carboxyl group and methyl group) in MCP were involved in the interaction between MCP and Cd²⁺. Molecular docking further demonstrated that polar and hydrophilic residues (e.g., aspartic acid, glutamic acid, serine, and histidine) on the surface of MCP bound to Cd²⁺ via electrostatic attraction. These findings offer new insights into Cd²⁺ bioremediation by MCP and genetic resources for microbial remediation of heavy metal pollution.