Exopolymeric substances production by Bacillus cereus KMS3-1 enhanced its biosorption efficiency in removing Cd2+ and Pb2+ in single and binary metal mixtures

The present study investigated the growth, exopolymeric substances production (EPS), and biosorption efficiency of Bacillus cereus KMS3-1 strain in the Cd2+ and Pb2+ ions containing single and binary metal-treated broth (50 mg/L). Furthermore, the interaction of KMS3-1 strain with Cd2+ and Pb2+ ions in single and binary metal-treated conditions was studied using SEM–EDS, FTIR, and XRD analyses. Results showed that, in both single and binary metal-treated broths, the biosorption efficiency (%) and EPS production of KMS3-1 biomass had increased with an increase in the incubation period and were observed higher for Pb2+ ions than for Cd2+ ions. In the single and binary metal-treated mediums, the maximum biosorption efficiency of KMS3-1 for Pb2+ ions was 70.8% and 46.3%, respectively, while for Cd2+ ions, it was 29.3% and 16.8%, respectively, after 72 h. Moreover, the biosorption efficiency of KMS3-1 strain for both metal ions was reliant on its EPS production and it peaked at maximum EPS production. The copious EPS production by KMS3-1 was noticed in metal-treated media (50 mg/L), which was in the following order of Pb2+ ions (1925.7 µg/mL) > binary metal mixtures (1286.8 µg/mL) > Cd2+ ions (1185.5 µg/mL), > control (1099 µg/mL) after 72 h of incubation. This finding revealed that KMS3-1 strain enhanced metal biosorption efficiency through increased EPS production in the surrounding metal-treated medium. SEM–EDS and FTIR characterization studies revealed that the KMS3-1 biomass effectively adsorbed Cd2+ and Pb2+ ions from the medium through interaction with their surface functional groups (hydroxyl, carbonyl, carboxyl, amide, and phosphate). Further, the bio-sorbed Cd2+ and Pb2+ ions were transformed into CdS and PbS, respectively by KMS3-1 biomass. The study suggests that the Bacillus cereus KMS3-1 strain could be a promising candidate to treat metal contamination.