Mechanism of a Cadmium-Lead Tolerant Phosphorus-Solubilizing Bacterium, Bacillus sp. PSB32, in Metal Removal and Plant Growth Promotion in Contaminated Systems
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1.College of Resources and Environment, Yunnan Agricultural University;2.College of Resources and Environment,Yunnan Agricultral University;3.Institute of Soil Science, Chinese Academy of Sciences

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Supported by the Natural Science Foundation of Yunnan Province, China (No. 202401AS070087), the National Natural Science Foundation of China (No. 42267002) and the Heavy Metal Pollution and Ecological Restoration in Lanping Lead-Zinc Mining Area, Observation and Research Station of Yunnan Pronvince, China (No. 2025AM340006)

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    Abstract:

    【Objective】Phosphorus-solubilizing bacteria (PSB) are ubiquitous in heavy metal-contaminated soils; however, their impacts on soil heavy metals and crop growth remain inadequately understood. 【Method】This study investigated the mechanisms and efficacy of Bacillus sp. PSB32, a Cd- and Pb-tolerant PSB strain isolated from the maize rhizosphere in the Yunnan Plateau, in removing aqueous Cd and Pb and influencing maize (Zea mays L.) growth in contaminated soils.【Result】Under Cd and Pb stress, strain PSB32 primarily removed Cd via intracellular accumulation(43.7%) and surface precipitation(43.2%), with biosorption playing a secondary role (13.0%). In contrast, Pb removal was dominated by surface adsorption (53.2%), followed by surface precipitation (28.8%) and intracellular accumulation (18.0%). Scanning electron microscopy (SEM) revealed the formation of granular precipitates on the bacterial cell surface, which were identified by X-ray diffraction (XRD) as Cd?(PO?)?, Pb?(PO?)?Cl (Pyromorphite), and Pb?(PO?)?OH. Fourier transform infrared (FTIR) spectroscopy confirmed the involvement of functional groups (e.g., -COOH, -OH, -NH?) and anionic groups (e.g., PO?3?, SO?2?) in the surface complexation of Cd and Pb. In the pot experiments, the amendment of PSB32 across the three differentially contaminated soils (contaminated farmland, tailings, and slag) led to a consistent increase of 5.90%-9.43% in the residual fraction of Cd, alongside a decrease of 7.20%-18.8% in the reducible fraction of Pb. Concurrently, the soil available phosphorus content was enhanced by 3.00%-18.7%, which contributed to a substantial promotion of maize biomass, ranging from 25.7% to 82.2%. Notably, PSB32 also increased the Cd content in maize shoots by 61.9% and 32.9% in the farmland and tailings soils, respectively, and significantly enhanced the accumulation of Cd and Pb in the roots by 365% and 35.3% in the slag soil.【Conclusion】In conclusion, Bacillus sp. PSB32 demonstrates a dual ecological function: effectively removing aqueous Cd and Pb through multiple mechanisms, and enhancing plant tolerance in contaminated soils by altering metal speciation and improving phosphorus nutrition. This strain presents a promising microbial resource for the bioremediation of heavy metal-contaminated soils.

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History
  • Received:August 03,2025
  • Revised:October 27,2025
  • Adopted:December 07,2025
  • Online: December 15,2025
  • Published:
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