Calcium Carbonate Crystals Formation by Ureolytic Bacteria Isolated from Australian Soil and Sludge

Abstract

Ureolytic bacteria were isolated selectively from sludge and soil samples (Perth, Western Australia). Three isolates were genetically examined by 16S rRNA. They were mostly closely related to Bacillus species. A bacterium producing the highest urease activity, Bacillus sp. MCP11 (DSM 23526), was used to precipitate calcium carbonate crystals. These crystals were precipitated due to bacterial activity in the presence of cementation solution (urea and calcium chloride, up to 1 M). Ureolytic bacteria hydrolyse urea producing carbonate and NH4+ causing an increase in the pH. In the presence of calcium ions in excess, calcium carbonate will precipitate. Type, size and shape of the precipitated calcium carbonate crystals were characterized by using light microscope and Scanning Electron Microscope (SEM). It was found that vaterite (spheres) and calcite (rhombohedral crystals) were precipitated at the surface of sand granules indicating the possibility of using those crystals to cement loose sand.