Paenibacillus polymyxa L62 synergistically regulates Pb2+ speciation and reconstructs soil microecological networks via surface complexation and PbS mineralization.

The adsorption activity of Paenibacillus polymyxa L62 toward Pb2+ was evaluated in aqueous systems. Strain L62 achieved a Pb2+ removal efficiency of 95.97%. Its cell surface was enriched with functional groups such as -OH and -COO⁻, which promoted Pb2+ adsorption via complexation and ion exchange. In aqueous systems, XRD, FTIR, and EDS analyses suggested the possible formation of stable PbS crystalline precipitates on the cell surface. In soil incubation experiments, strain L62 was inoculated into Pb-contaminated soil at 1% (L1) and 3% (L3). Both treatments significantly promoted Pb transformation among different fractions, with L3 showing greater efficacy. Compared with the control, L3 increased soil cation exchange capacity and soil organic matter by 55.24% and 5.26%, respectively. Microbial community analysis showed that L1 and L3 enriched key bacterial genera, including Marinobacterium and Photobacterium, and significantly enhanced soil acid phosphatase, urease, and dehydrogenase activities. Collectively, P. polymyxa L62 removed Pb2+ in aqueous systems mainly through surface complexation and possible PbS mineralization. In soil, L62 promoted Pb transformation toward more stable fractions and reshaped the microbial community and enzyme activities.