Assessment of a biostimulated or bioaugmented calcification system with Bacillus pasteurii in a simulated soil environment.

To evaluate how native soil microorganism and nutrients interact in a bioaugmented or biostimulated calcification process, batch experiments were conducted in saturated soil extract either amended with Bacillus pasteurii and/or NB-NH4Cl media (nutrient broth, 3.0 g/L; NH4Cl, 10.0 g/L; NaHCO3, 2.12 g/L). The NB-NH4Cl medium was chosen out of three potential candidates, where B. pasteurii precipitated the maximum amount of calcium (>95 %) as calcite in 12 h of incubation. The addition of B. pasteurii into saturated soil extract marginally improved the calcification to 4.26 % compared to the unamended control (3.2 %). Calcification with B. pasteurii in autoclaved soil extract was even better (18.75 %). However, the addition of the NB-NH4Cl medium into the soil extract could significantly improve the calcification irrespective of whether B. pasteurii was added (88.46 %) or not (77.04 %). It suggests that soil microbial activity was not limiting even though soil nutrient was inadequate. It also indicates a possible negative interaction between soil microorganisms and B. pasteurii under nutrient-limited conditions.