Isolation, Identification and Preliminary Remediation Performance Evaluation of Heavy Metal-Tolerant Bacteria from the Mining Area in Northern Shaanxi

Abstract

To address heavy metal contamination in soils of the northern Shaanxi coal mining area, this study directionally screened and isolated a functional bacterial strain, Bacillus sp. NM-1, tolerant to Mn2+, Fe3+, and Cr6+, from polluted soil collected in the Shenmu mining region, Shaanxi Province, China. The isolate was identified as Bacillus sp. based on 16S rRNA gene sequencing analysis. A subsequent pot experiment was conducted to systematically evaluate the remediation efficacy of the selected strain in manganese-contaminated soil. Among the six metal-tolerant strains obtained, strain NM-1 exhibited the highest removal efficiency and the broadest concentration adaptability for Mn2+, Fe3+, and Cr6+, achieving over 99.5% removal of Mn2+ at an initial concentration of 100 mg/L. Subcellular distribution analyses of intracellular and extracellular ions, together with inactivated cell controls, revealed that extracellular adsorption constituted the primary mechanism underlying heavy metal removal. In the pot experiment, manganese ion (Mn2+) was used as the model contaminant. The results demonstrated that inoculation with NM-1 significantly alleviated manganese-induced growth inhibition in maize plants, as evidenced by increased plant height, biomass, and photosynthetic pigment content. Furthermore, NM-1 inoculation reduced malondialdehyde (MDA) accumulation while enhancing peroxidase (POD) activity and proline content, thereby improving the plant’s antioxidant capacity and osmotic regulation. Overall, this study provides a multifunctional metal-tolerant bacterial strain that represents a valuable microbial resource and offers theoretical support for microbe–plant combined remediation strategies in heavy metal-contaminated soils of the northern Shaanxi mining region.