Mechanism of carbonate mineralization induced by microbes: Taking Curvibacter lanceolatus strain HJ-1 as an example

Microbial-induced carbonate precipitation is important in the global carbon cycle, especially in fixing atmospheric CO₂. Many simulation experiments have shown that microbes can induce carbonate precipitation, although there is no established understanding of the mechanism. In this study, several mineralization experiments were performed using Curvibacter lanceolatus strain HJ-1, including its secreted extracellular polymeric substances (EPS) and carbonic anhydrase (CA). We found that strain HJ-1, EPS, and CA could promote carbonate precipitation if compared with the respective control experiments (CK). Also, both HJ-1 and EPS1 experiments contained calcite and aragonite, whereas CA experiments formed calcite only. Therefore, HJ-1 and EPS is favorable for carbonate precipitation, especially for aragonite. Besides, the formation of calcite in the EPS2 experiments indicated that EPS contains a trace amount of CA, which might promote CO₂ hydration and eventually lead to carbonate precipitation. It was suggested that CA only provide CO₃^2- for the formation of carbonate minerals. In the absence of exogenous HCO₃-, the optimized calcification rate followed the order: HJ-1(49.5 %) > CA(6.6 %) > EPS2(4.1 %). In addition, MICP mechanisms was studied, an increase in pH and CO₂ hydration by CA play synergetic roles in providing supersaturated alkaline conditions in the system with bacteria. Finally, bacterial cells and EPS promote the formation of calcite and aragonite by acting as nucleation sites.