Abstract
Biomineralization induced by microorganisms has become a hot spot in the field of carbonate sedimentology; however, the mechanisms involved still need to be explored. In this study, the bacterium Bacillus subtilis J2 (GenBank MG575432) was used to induce the precipitation of calcium carbonate minerals at Mg/Ca molar ratios of 0, 3, 6, 9, and 12. Bacillus subtilis J2 bacteria released ammonia to increase pH, but the ammonia released only made the pH increase to 8.25. Carbonic anhydrase was also produced to catalyze the hydration of carbon dioxide, and this process released carbonate and bicarbonate ions that not only increased pH but also elevated carbonate supersaturation. The biominerals formed at a Mg/Ca molar ratio of 0 were spherulitic, elongated, dumbbell-shaped, and irregularly rhombohedral calcite; at a Mg/Ca molar ratio of 3, the biominerals were calcite and aragonite, the weight ratio of calcite decreased from 26.7% to 15.6%, and that of aragonite increased from 73.3% to 84.4% with increasing incubation time. At higher Mg/Ca molar ratios, the biominerals were aragonite, and the crystallinity and thermal stability of aragonite decreased with increasing Mg/Ca molar ratios. FTIR results showed that many organic functional groups were present on/within the biominerals, such as C–O–C, N–H, C=O, O–H, and C–H. HRTEM-SAED examination of the ultra-thin slices of B. subtilis J2 bacteria showed that nano-sized minerals with poor crystal structure had grown or been adsorbed on the EPS coating. The EPS of the B. subtilis J2 strain contained abundant glutamic acid and aspartic acid, which could be deprotonated in an alkaline condition to adsorb Ca2+ and Mg2+ ions; this made EPS act as the nucleation sites. This study may provide some references for further understanding of the mechanism of biomineralization induced by microorganisms.
Highlights
Biomineralization refers to the process where the formation of certain kinds of inorganic minerals can be regulated by some organisms
Sulphate-reducing bacteria (SRB) and halophilic bacteria have been used to induce the precipitation of dolomite [56], and the results have shown that these extracellular polymeric substances (EPS)-like materials may have served as an additional template for dolomite nucleation, since no dolomite was detected in experiments containing heat-killed bacteria due to the absence of EPS materials
The B. subtilis J2 bacterium was used in experiments to induce the precipitation of calcium carbonate at Mg/Ca molar ratios of 0, 3, 6, 9 and 12
Summary
Biomineralization refers to the process where the formation of certain kinds of inorganic minerals can be regulated by some organisms. The biggest difference between biomineralization and general mineralization lies in the participation of bio-macromolecular metabolism, cells, and organic matrix. The precipitation of calcium carbonate (CaCO3 ) induced by microbes is a common process in aquatic environments [22,23,24,25,26,27]. Recent literature has shown that the precipitation of calcite minerals by microbes within the pores of a rock can quickly reduce its permeability to water [29]. Besides restricting the water penetration, the product of biomineralization induced by bacteria can limit the exchange between the pores of the limestone and the atmosphere to protect the rock [31]. Based on the discovery of biomineralization, researchers have begun to develop new cementing materials
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