Insight into mineral-microbe interaction on cadmium immobilization via microbially induced phosphate precipitation...

Microbially induced phosphate precipitation (MIPP) is a promising strategy for cadmium (Cd) immobilization. However, the role of phosphorus source composition in regulating biomineralization efficiency and the influence of phosphate-solubilizing bacteria (PSB) on the soil microbiology for Cd immobilization remain insufficiently understood. This study investigates the Cd immobilization potential of PSB in combination with three phosphate minerals, including calcium phosphate (CP), phosphate rock (PR), and hydroxyapatite (HAP). A highly effective strain, Pseudomonas sp. ML1, was isolated for its remarkable Cd tolerance and phosphate solubilization capacity. Compared to CP-ML1 and PR-ML1, HAP-ML1 achieved the highest Cd removal efficiency, reaching 99.90 % within 24 h. The immobilization products formed by HAP-ML1 were mainly Ca_4.03Cd_0.97(PO₄)₃OH and (Ca_7.7Cd_0.5) (PO₄)₆(H₂O)_2.4, which exhibited superior stability under conditions ranging from pH 1.0-9.0. In addition, functional groups and EPS precipitate in Cd immobilization in the mineral-microbe hybrid systems. In soil, the HAP-ML1 treatment decreased the Cd bioavailability. Meanwhile, it increased the available phosphorus (AP) content, phosphatase activity, and the relative abundance of phosphate-solubilizing genes and Cd resistance genes. The abundance of phosphate-solubilizing genes gcd and phoD increased by 102.37 % and 89.71 %, respectively. The efficient and stable release of phosphate by HAP-ML1 for Cd immobilization, along with the microbial ecological regulation mechanisms involved, highlights the potential of HAP-ML1 in remediating Cd-contaminated soils.