Lead (Pb) bioremediation by Sphingobium sp. RO-01 strain isolated from gold mine tailings, Atacama Desert, Chile.

This study investigated the microbiological and geochemical characteristics of gold mining tailings and assessed the potential of a Pb-tolerant bacterial strain, Sphingobium sp. RO-01, for lead (Pb) removal through biomineralization. The tailings were dominated by fine particles (average 12.3 μm) with low permeability and high leaching potential, indicating a substantial risk of heavy-metal dispersion and acid mine drainage. X-ray fluorescence analysis showed Pb concentrations of 580 ppm, exceeding the EPA limit of 400 ppm, while X-ray diffraction suggested that Pb was primarily present in amorphous or adsorbed phases. Mineralogical data indicated that most Pb was associated with pyrite, jarosite, and Fe oxides-hydroxides. Microbial community profiling revealed Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria as the dominant phyla, consistent with microbial assemblages typically adapted to heavy-metal stress. The isolated Sphingobium sp. RO-01 strain, a urease-positive bacterium capable of tolerating up to 10 mM Pb, removed approximately 82% of soluble Pb after 48 h under planktonic conditions. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) confirmed Pb incorporation into CaCO₃ biominerals, indicating urease-mediated microbially induced calcite precipitation (MICP) as the principal immobilization mechanism. Furthermore, the strain substantially reduced the genotoxicity associated with soluble Pb, likely due to its transformation into stable mineral phases and the production of extracellular substances that mitigate oxidative stress. Overall, these findings highlight Sphingobium sp. RO-01 as a promising biotechnological tool for the remediation and stabilization of Pb-contaminated mining environments.