Development of microbial biosorbents based on homologs of cadmium-resistant regulators for efficient cadmium removal:...

This study aims to develop whole-cell biosorbents displaying cadmium-resistant regulator (CadR) homologs for efficient cadmium (Cd) removal from environmental waters. Cadmium pollution poses significant threats to ecosystems and human health due to its toxicity, persistence, and tendency to bioaccumulate. Although biological remediation has been extensively researched, approaches targeting complex environmental matrices are not commonly reported. By leveraging natural gene repositories, we constructed a library of CadR homologs-displaying bacteria and identified CadR10 as a highly efficient and selective Cd(II) adsorbent. Specifically, the CadR10-displaying strain effectively captured Cd(II), as demonstrated by Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy (TEM-EDX) and bead-binding assays. Notably, the presence of other metal ions, such as Pb(II), Hg(II), and Zn(II), did not significantly affect the Cd(II) adsorption capacity of the CadR10 strain, thereby demonstrating its high selectivity for cadmium. The q_max for the strain expressing InaPb-CadR10 was determined to be 0.649 mg/g of biomass. This unprecedented application attempt highlights the potential of CadR10 in environments with multiple metal ions, such as seawater. The CadR10-displaying strain significantly removed Cd(II) from 50 % and 100 % seawater solutions, showcasing its robust performance in complex matrices. Our findings provide a proof-of-concept for the selective removal of cadmium via surface-engineered environmental microorganisms, highlighting the potential of biological macromolecules in future marine microbe-based bioremediation strategies.