Distinct and indispensable roles of cell viability and extracellular polymeric substances in Pb mineralization by Sinorhizobium sp. C10.

Microbially induced phosphate mineralization (MIPP) is a promising strategy for immobilizing lead (Pb) in contaminated environments. This study aimed to determine whether cell viability and EPS are indispensable for Pb mineralization by Sinorhizobium sp. C10, a strain previously shown to form lead phosphate minerals. We compared live versus heat-inactivated cells, employed a mild sodium citrate method to strip EPS while preserving cell viability, and determined Pb removal efficiency, alkaline phosphatase (ALP) activity, inorganic phosphate (PO43-) release, and mineral phase composition. Live C10 cells removed up to 99.8% of Pb from solution (initial concentrations: 50 and 150 mg/L) within 26 h and formed crystalline Pb5(PO4)3Cl. In contrast, heat-inactivated cells showed negligible ALP activity, failed to release Pi, and did not induce mineral formation. Despite retained cell viability, EPS stripping resulted in a marked reduction in Pb and P elemental signals on cell surfaces, along with diminished intensity of functional groups (e.g., P-O, C = O, -OH) critical for Pb binding. These findings demonstrate that both active cellular metabolism (specifically ALP-mediated Pi release) and intact EPS (providing essential functional groups) are indispensable for Pb biomineralization by Sinorhizobium sp. C10. Importantly, these two mechanisms are closely interlinked rather than independent: ALP-mediated metabolism generates phosphate ions that provide the chemical driving force for biomineralization, while EPS-itself a metabolic product-serves as a physical scaffold for Pb2+ adsorption and mineral nucleation. Together, active metabolism and intact EPS synergistically promote Pb5(PO4)3Cl formation.