Cell viability and extracellular polymeric substances are indispensable for Pb mineralization by Sinorhizobium sp. C10

Lead (Pb) pollution is a pressing global environmental problem due to its threat to ecosystem health. Rhizobia have garnered significant interest since they demonstrate potential to clean up Pb contaminated soils. However, the processes by which rhizobia mediate Pb biomineralization are not well understood. In this study, sp. (C10) isolated from a soil near a mining site, was used to explore the mechanisms of Pb biomineralization facilitated by this strain, with a particular focus placed on the roles of cell viability and extracellular polymeric substances (EPS). It was found that the strain could sustain growth and metabolic functions under Pb stress. The Pb removal rate reached 99.8% after 26 h of with 50 and 150 mg/L Pb treatments. The alkaline phosphatase from C10 cells effectively decomposed organophosphorus compounds in the culture and released soluble phosphate (P), forming stable chloropyromorphite (Pb5(PO4)3Cl). In contrast, heat-inactivated C10 lost the function of secreting alkaline phosphatase and could not form Pb mineral on the cell surface. Moreover, after stripping EPS, the signal intensities of Pb and P were significantly reduced, as evidenced in the SEM-EDS analysis. Overall, these findings confirmed that cell viability and EPS are indispensable in Pb biomineralization induced by C10.