Study of the interactions between S. pasteurii and indigenous bacteria and the effect of these interactions on the MICP

A new soil improvement method, called microbial-induced calcite precipitation (MICP), has recently emerged, which is based on microbial mineralisation by injecting bacteria solution and nutrient into soil for the purpose of modifying physico-mechanical properties. Since the MICP process in natural soils is likely to be impacted by the interactions between Sporosarcina pasteurii and indigenous bacteria, we herein examine these interactions and their effects on MICP. The soil extract was used as a source of natural microorganisms, and a control treatment was inoculated in an artificial solution, based on the soil extract with no microorganisms. The following parameters were monitored in the whole process of the experiments: optical density (OD), pH, dissolved Ca 2+ and dissolved inorganic carbon (DIC). The results show that dissolved Ca 2+ precipitate as CaCO 3 more quickly in the control than in natural soil extract. S. pasteurii exhibits a significantly higher growth rate in the artificial soil extract than in the natural solution, which results in a higher density of bacterial cells. We suggest that the presence of the indigenous bacteria decelerates the MICP process by competing with S. pasteurii for nutrients.