Bioremediation using soil indigenous ureolytic bacteria

The ubiquity of bacteria and the diverse roles they play in natural environments have led to the growing interest in harnessing bacterial activities for various anthropogenic purposes. Microbial-induced calcite precipitation (MICP) is an emerging technique aimed at addressing different environmental and engineering concerns, including soil stabilization, healing cracks in concrete, and remediation of contaminated soils and aquifers, among others. This technique is based on urea hydrolysis catalyzed by the microbial urease enzyme, which produces ammonium and carbonate, increases calcium carbonate concentrations, and leads to calcium carbonate precipitation, usually as calcite.

In the present study, MICP using indigenous ureolytic bacteria enriched from the Yamin plateau at the north-eastern Negev Desert was evaluated for its potential to remediate strontium from groundwater. Indigenous ureolytic bacteria were enriched from coarse-grained sand sampled from the Yamin plateau. Enrichments of ureolytic bacteria were verified by the depletion of urea from the media and a significant increase in pH, which are typical hallmarks of MICP. Bioremediation experiments using the enriched bacteria demonstrated the formation of calcium- and strontium- carbonate precipitates. Calcium and strontium ion concentrations were depleted after three days only, as shown by inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. Dried precipitates were analyzed by X-ray powder diffraction (XRD), showing they were mainly composed of calcite and vaterite.

Taken together, our study shows that indigenous urea-hydrolyzing bacteria are naturally present in the Yamin plateau of the north-eastern Negev Desert in Israel. It demonstrates that indigenous bacteria can be readily stimulated to hydrolyze urea and induce strontium immobilization for the purpose of groundwater bioremediation.