Heavy metal removal by biomineralization of urease producing bacteria isolated from soil

Microorganisms can mediate the formation of minerals by a biomineralization process. This offers an efficient way to sequester inorganic pollutants, including heavy metals within relatively stable solid phases, and the main mechanisms involved in mineral precipitation by microorganisms were investigated in this study. Biomineralization of nickel, copper, lead, cobalt, zinc and cadmium, by six metal-resistant bacterial strains, were investigated using microcosm experiments. These bacteria were isolated from nursery garden soil and characterized for their potential application in bioremediation. These bacteria produced the enzyme urease which can hydrolyze urea. Due to this enzymatic reaction, soil pH increased and carbonate was produced, which results in mineralization of the soluble heavy metal ions present in soil water and their ultimate conversion to carbonates. The selected bacteria showed high removal rates, ranging from 88% to 99% of heavy metals following incubation for 48 h. Scanning electron microscopy and X-ray diffraction analyses revealed that bioaccumulated heavy metals ions were deposited around the cell envelope as rhombohedral, sphere and needle shaped crystalline carbonate minerals when the pH was 8–9. This study demonstrated that indigenous bacteria can survive heavy metal toxicity from soil and wastewater and sequester soluble heavy metals into biominerals and these bacteria can play important role in heavy metal bioremediation.