Ureolytic Calcium Carbonate Precipitation in the Presence of Non-Ureolytic Competing Bacteria

Stimulation of ureolytic Microbially Induced CaCO₃ Precipitation (MICP) in natural soils is likely to be affected by interactions between ureolytic and non-ureolytic bacteria. In order to study these interactions we performed a MICP experiment in artificial groundwater medium, inoculated with two model bacteria: Sporosarcina pasteurii and Bacillus subtilis, and supplemented with Nutrient Broth and 7 mM of urea. Control was inoculated with S. pasteurii. The experiment lasted 10 days, during which ammonium, dissolved calcium, pH, dissolved inorganic carbon (DIC) and optical density (OD) were measured. Results show that dissolved calcium was depleted at a higher rate in the presence of non-ureolytic bacteria, despite lower pH and CO₃^2– concentration. OD measurements show higher growth rate than in control samples. We suggest that the presence of the non-ureolytic bacteria, B. subtilis, accelerates MICP process, through the addition of nucleation sites in the form of bacterial cells.