Phosphorus solubilizing bacteria Bacillus thuringiensis and Pantoea ananatis simultaneously promote soil inorganic phosphate dissolution and soil Pb immobilization

The phytoavailability of lead (Pb) can be greatly reduced when Pb forms stable phosphate compounds in soil. This study employed broth culture, soil incubation, and pot experiments to investigate whether phosphate solubilizing bacteria (PSB) could effectively immobilize soil Pb through dissolution of insoluble inorganic P compounds. The results showed that both Bacillus thuringiensis GL-1 (GL-1) and Pantoea ananatis HCR2 (HCR2) could use Ca-3(PO4)(2), FePO4, and A1PO 4 as the sole P resource and significantly increase water-soluble phosphate concentrations, which reached 555.84 and 392.66 mg/L, 13.82 and 72.06 mg/L, and 93.29 and 92.87 mg/L, respectively. The minimum pH of these culture media was reduced to 3.93 and 4.02, 3.37 and 3.40, and 2.86 and 2.89, respectively. Compared with the control, inoculation of GL-1 to artificially Pb-contaminated soil significantly reduced Fe-P, Al-P, Olsen-P, and NH4NO3-extractable Pb concentrations by 13.70%, 15.84%, 13.29%, and 33.61%, respectively, while reduced those by 23.75%, 53.43%, 11.66%, and 47.54% in the case of HCR2. Similarly, inoculation of GL-1 or HCR2 significantly reduced Fe-P concentrations of the historically metalcontaminated acidic soil by 50.00% and 46.73%, respectively. The NH4NO3 -extractable soil Pb concentrations also decreased, which was only significant in soil inoculated with GL-1. Pot experiment found that inoculation of GL-1 and HCR2 decreased soil Pb phytoavailability and consequently inhibited its uptake by lettuce (Lactuca sativa L.). Meanwhile, the inoculation of HCR2 significantly promoted plant growth and reduced shoot Pb concentrations when grown in artificially Pb-contaminated soil. The results suggest that inoculation of GL-1 and HCR2 could be applied for remediating Pb-contaminated soils.