Mechanisms of carbonate precipitation induced by two model bacteria

The investigation of microbially induced calcium carbonate precipitation is essential to understanding CO2 fixation, marine carbonate rock formation, and biogeochemical cycling of life-essential elements. In this study, two model bacteria Bacillus subtilis (possess the cell wall of G+ bacteria) and Escherichia coli (possess the cell wall of G− bacteria) were used as representatives to induce carbonate mineralization. The mineralization ability of the two bacteria and carbonate precipitation mechanisms were studied with the biochemical analysis of bacterial fermentation products, mineral characterization, and biomimetic mineralization experiments. The results showed that both bacteria induced biomineral formation by using the cell wall as a template, but B. subtilis was more capable of inducing mineralization than E. coli. Particularly, the percentage of Ca2+ removal from the culture medium by the former reached 36% in 7 days, which induced the formation of vaterite and calcite, while that of Ca2+ removal by the latter reached 28%, and the resulting carbonate was amorphous calcium carbonate. Biomimetic mineralization experiments showed that protein molecules were the key factors inducing the formation of biological vaterite, while polysaccharides tended to bind small vaterite particles to form large organo-mineral aggregates. By comparing the results of inducing calcium carbonate under the same culture conditions, the two types of bacteria with completely different cell wall structures had significant differences in the ability to induce calcium carbonate synthesis, among which that was stronger by Bacillus subtilis (G+) than by Escherichia coli (G−). It was found that factors such as bacterial cell wall structure, extracellular secretions including carbonic anhydrase, pH value, etc. all affect the microbial-induced carbonate precipitation to varying degrees, providing new insights into the theory of bacterial-induced carbonate mineralization.