Bioremediation potential and primary mechanism of Sporosarcina pasteurii for cadmium (Cd) and lead (Pb) in contaminated tailings

ABSTRACT Efficient bioremediation technology has drawn extensive attention from scholars due to the serious damage caused by heavy metals (HMs) to the environment. This study explored the remediation potential and mechanisms of the S. pasteurii strain in alleviating toxicity of Cd and Pb in tailings. The results showed that the decrease in DTPA-Cd and -Pb was associated with the transfer of exchangeable HMs to carbonate-bound HMs in bacteria-treated tailings. Biomineralization, extracellular adsorption, and intracellular accumulation were observed to result in removal rates above 95% for HMs in tailings solution. Mineralisation products driven-urease were identified as carbonate minerals, including otavite CdCO3, cerussite PbCO3 and hydrocerussite Pb3(CO3)2(OH)2. However, the increased Km in the urease kinetics study indicated that HMs reduced urease activity and biomineralization by minimum inhibitory concentrations (Cd 0.5 mM and Pb 40 mM). The functional groups (-OH, -NH2, -COOH and -PO4 3-) on the bacterial surface were involved in immobilising HMs, while the biosorption capacity (qm) was inhibited by metal ions (Pb2+ > Cd2+) according to Langmuir sorption isotherm. In conclusion, the biomineralization-adsorption of S. pasteurii was the mainstay for stabilising Cd and Pb in tailings, and the contribution of biomineralization was found to be much higher than that of biosorption.