## 1 Introduction
[18] also found that strontium could coprecipitate with calcite generated by bacterial ureolysis, and the extent of the strontium incorporation appeared to be driven primarily by the overall rate of calcite precipitation. [PERSON] and [PERSON] [21] studied the effect of temperature (i.e., 10, 15 and 20 \({}^{\circ}\)C) and time on the coprecipitation of strontium into calcite precipitates induced by bacterial ureolysis, and found that higher coprecipitation efficiency occurred at 20 \({}^{\circ}\)C. [PERSON] et al. [19] used laboratory-scale porous media flow cells to study the coprecipitation of strontium in carbonate minerals via ureolysis by _S. pasteurii_, and found that coprecipitation was effective (56-59%) under both pulsed and continuous flow scenarios. [PERSON] et al. [38] found that the immobilization ratio of heavy metals copper, lead, zinc, cadmium and nickel were above 88% at the initial concentration of 2 g/L. [PERSON] and [PERSON] [20] studied coprecipitations of a few heavy metals with calcium and found that _S. pasteurii_ was not effective for the removal of copper (30%) in contrast with the removal efficiencies of lead, zinc and cadmium. [PERSON] et al. [39] found that the calcium source and initial bacteria concentration had a significant influence on the lead immobilization efficiency, and the best removal ratio could be over 95%. [PERSON] et al. [40] found that _S. pasteurii_ could eliminate 98.71% of lead, 97.15% of cadmium and 94.83% of zinc. [PERSON] et al. [36] found a low removal ratio of copper (10%) in water through MICP using _S. pasteurii_, and attributed it to copper complexation with the ammonia generated by the urea hydrolysis. [PERSON] et al. [35] found that Cd\({}^{2+}\) removal efficiency could be greatly improved by the supplement of Ca\({}^{2+}\) and nearly all the cadmium ions in the solution could by removed. [PERSON] et al. [41] studied the removal behaviors of divalent cations when coprecipitated with calcium, and found that Pb\({}^{2+}\) and Sr\({}^{2+}\) had a high removal efficiency of more than 99%, while Cu\({}^{2+}\), Zn\({}^{2+}\) and Cd\({}^{2+}\) demonstrated a low removal efficiency of 30-60% at an initial concentration no greater than 0.05 mM. [PERSON] et al. [1] found that _S. pasteurii_ could immobilize cadmium, chromium and zinc very effectively in aqueous solutions, while the immobilization efficiency for copper and nickel was very low, especially for copper. From the studies above, we can observe that significant progress has been made in removing heavy metals from aqueous solutionsby _S. pasteurii_, and carbonate ions can promote the coprecipitaion of heavy metals in high pH environments. However, the results sometimes were very different from each other according to the removal efficiency. Moreover, the majority of the experiments were carried out at low heavy metal concentrations (0.01-1 mmol/L) due to the high toxicity of heavy metals to the bacteria [35; 41; 42]. Microbially induced carbonate precipitation was considered as a complex process, and both environmental conditions and biotic factors could affect the precipitation process. We can observe from the above studies that the effects of external factors such as pH, temperature, time and heavy metal concentration on the removal of heavy metals by _S. pasteurii_ were mainly discussed, while the urea concentration of culture substrate and the calcium concentration should be taken into account simultaneously in view of the huge differences among those reported studies. Thus, in this study we designed a series of experiments to acclimatize _S. pasteurii_ in heavy metal amended nutrient broths in order to improve the resistance of _S. pasteurii_ to a heavy metal environment, to consider urea concentration and Ca\({}^{2+}\) concentration in detail and to study the removal behaviors of different concentrations of heavy metals (i.e., Cd\({}^{2+}\), Cu\({}^{2+}\) and Pb\({}^{2+}\)) by _S. pasteurii_.