Accelerated microbial-induced CaCO₃ precipitation in a defined co-culture of ureolytic and non-ureolytic bacteria

Microbial-induced CaCO₃ precipitation (MICP) is an innovativetechnique that harnesses bacterial activity for the modification of thephysical properties of soils. Since stimulation of MICP by ureahydrolysis in natural soils is likely to be affected by interactionsbetween ureolytic and non-ureolytic bacteria, we designed an experimentto examine the interactions between ureolytic and non-ureolytic bacteriaand the effect of these interactions on MICP. An artificialgroundwater-based rich medium was inoculated with two model species ofbacteria, the ureolytic species Sporosarcina pasteurii and thenon-ureolytic species Bacillus subtilis. The control treatment wasinoculated with a pure culture of S. pasteurii. The following parameterswere monitored during the course of the experiment: optical density, pH,and the evolution of ammonium, dissolved calcium, and dissolvedinorganic carbon. The results showed that dissolved calcium wasprecipitated as CaCO₃ faster in the mixed culture than in thecontrol, despite less favorable chemical conditions in the mixedculture, i.e., lower pH and lower CO32-concentration. B. subtilis exhibited a considerably higher growth ratethan S. pasteurii, resulting in higher density of bacterial cells in themixed culture. We suggest that the presence of the non-ureolyticbacterial species, B. subtilis, accelerated the MICP process, via thesupply of nucleation sites in the form of non-ureolytic bacterial cells.