Ureolysis and MICP with model and native bacteria: Implications for treatment strategies

We present results from experiments of microbially induced calcite precipitation (MICP) in co-cultures of model bacteria and results of experiments studying the ureolytic potential of native bacterial extracts. The model co-cultures experiments were designed to study possible interactions associated with introduction of exogenous ureolytic bacteria into a native soil. It was found that in co-cultures of ureolytic bacteria, S. pasteurii, with increasing concentrations of nonureolytic bacteria, B. subtillis, the rate of ureolysis and the rate of calcite precipitation increased with the concentration of B. subtillis. We postulate that the increased rates are attributed to release of urease by S. pasteurii in response to nutrient stress conditions or predation by B. subtillis. Coastal sand was tested for ureolytic capacity and nitrification potential. It was found that urea hydrolysis rate depend on nutrient media used, and that nitrifying bacteria are present in the sampled sand. Urea concentration optimization experiment performed using the bacterial extract showed that the minimal concentration of urea (supplemented with 1 gr/liter molasses) required for efficient hydrolysis is 200 mM and that for 300 mM of urea hydrolysis rate is higher by a factor of 3. These results compare well with previously reported for the model bacteria S. pasteurii.