Biosequestration of heavy metals by microbially induced calcite precipitation of ureolytic bacteria

Microbial induced calcite precipitation (MICP) using urease producing bacteria has gained great importance of research in recent years. In this study, the efficiency of ureolytic, heavy metals resistant bacteria to biomineralize toxic heavy metals has been investigated. Twenty two bacterial strains were isolated from calcareous soil samples collected from Egypt and screened for urease and calcite production as well as the tolerance to heavy metals toxicity. Micrococcus sp. NCTC -1716 was selected for subsequent studies as it was the most potent strain. Resistance of Micrococcus to increasingly concentrations of zinc, cadmium, lead and iron varied according to the metal. The capacity of Micrococcus sp. to remove heavy metals ranged from 60.66 % for Cd2+ to 97.20 % for Pb2+ after 48 h of incubation. Metal sequestration via calcite precipitation showed that heavy metals are removed according to the following sequence: Pb2+, Fe2+, Zn2+, and Cd2+. Scanning electron microscope was used to examine the morphology of calcite crystals and biomineralization products, while their structure was emphasized by X-ray diffraction (XRD) analysis. The study confirmed that MICP sequesters soluble heavy metals into biominerals and proved as a promising strategy for bioremediation process.