Biomineralization has become a research hotspot and attracted widespread attention in the field of carbonate sedimentology. In this study, precipitation of carbonate minerals was induced by Bacillus licheniformis
DB1-9 bacteria, (identity confirmed with its phylogenetic tree), to further explore the biomineralization mechanisms. During experiments, lasting up to 24 days with varying Mg/Ca molar ratios and regular monitoring of conditions, ammonia and carbonic anhydrase are released by the bacteria, resulting in a pH increase. Carbonic anhydrase could have promoted carbon dioxide hydration to produce bicarbonate and carbonate ions, and so promoted supersaturation to facilitate the precipitation of carbonate minerals. These include rhombohedral, dumbbell-shaped, and elongated calcite crystals; aragonite appears in the form of mineral aggregates. In addition, spheroidal and fusiform minerals are precipitated. FTIR results show there are organic functional groups, such as C–O–C and C=O, as well as the characteristic peaks of calcite and aragonite; these indicate that there is a close relationship between the bacteria and the minerals. Ultrathin slices of the bacteria analyzed by HRTEM, SAED, EDS, and STEM show that precipitate within the extracellular polymeric substances (EPS) has a poor crystal structure, and intracellular granular areas have no crystal structure. Fluorescence intensity and STEM results show that calcium ions can be transported from the outside to the inside of the cells. This study provides further insights to our understanding of biomineralization mechanisms induced by microorganisms.
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