Application of phosphate solubilizing bacteria in immobilization of Pb and Cd in soil

In the present study, heavy metal (HM)-tolerant phosphate solubilizing bacteria (PSB) were isolated and their performance during the remediation of Pb and Cd in contaminated soil was studied. A total of 16 bacterial strains and one consortium were isolated, and the consortium had the highest phosphate solubilizing ability and HM tolerance. Great variations between the Fourier transform infrared (FTIR) spectra of consortium cells before and after adsorption of Pb2+ and Cd2+ revealed that amide I/amide II bonds and carboxyl on the cell surface were involved in binding of metal ions. High-throughput sequencing technique revealed that the consortium was composed of Enterobacter spp., Bacillus spp., and Lactococcus spp. The consortium was added into contaminated soil, and its potential ability in dissolution of phosphate from Ca-3(PO4)(2) and subsequent immobilization of HMs was tested. Results showed that when Ca-3(PO4)(2) was applied at 10.60 mg/g soil, PSB addition significantly increased soil available phosphate content from 12.28 to 17.30 mg/kg, thereby enhancing the immobilization rate of Pb and Cd from 69.95 to 80.76% and from 28.38 to 30.81%, respectively. Microcalorimetric analysis revealed that PSB addition significantly improved soil microbial activity, which was possibly related with the decreased HMs availability and the nutrient effect of the solubilized phosphate. The present study can provide a cost-effective and environmental-friendly strategy to remediate multiple HM-contaminated soils.