Extracellular and Intracellular Biomineralization Induced by Bacillus licheniformis DB1-9 at Different Mg/Ca Molar Ratios

Abstract

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.

Bio-Precipitation of Carbonate and Phosphate Minerals Induced by the Bacterium Citrobacter freundii ZW123 in an Anaerobic Environment

“…The adsorption peaks at 712, 875 and 1421 cm −1 are the characteristic peaks of calcite, and the characteristic peaks of vaterite are at 745, 870 and 1421 cm −1 [2,7]. In addition, the peaks at 700, 765, 872, 1064, 1401 and 1480 cm −1 record the presence of monohydrocalcite [7,58]. Characteristic peaks of struvite include the H-O-H group for water molecules at 1656 cm −1 ; the symmetrical and asymmetrical bending vibration of N-H (NH + 4 ) at 1609 and 1439 cm −1 ; the asymmetrical stretching vibration of PO 3− 4 at 1003.79 and 571.78 cm −1 ; the symmetrical bending vibration of PO 3− 4 at 453.16 cm −1 ; the hydrogen bond between waters at 762.4 cm −1 and the hydrogen bond between ammonium and water at 886.70 cm −1 [22,32].…”

“…CA activity then showed a slight decline from 60 h to 156 h. From Figure 1b, it can be concluded that there was still a large amount of CA in the fluid even during the decline stage of ZW123 bacteria (Figure 1a). CA can catalyze the hydration of carbon dioxide to release bicarbonate and carbonate ions [32,58]. The concentration of bicarbonate increased from 0.02 mol/L to 0.036 mol/L in the first 48 h, declined from 0.036 mol/L to 0.0163 mol/L in the time range of 48-96 h, then almost remained stable until 156 h. Coinciding with the decline of the bicarbonate, the presence of carbonate was first detected at 72 h; the concentration of carbonate then increased from 0.007 mol/L to 0.019 mol/L in the time range of 72-96 h, and then remained nearly stable.…”

“…NH 3 is also produced in the degradation process of organic substances in the culture medium through the microbial metabolism. Released NH 3 can not only lead to an increase in pH [33] but also be involved in the formation of struvite as one of the components [29,58], which is necessary for the mineral precipitation. The stable isotope studies further emphasize the important role that microorganisms play in the bio-precipitation process of biotic minerals.…”

Bio-Precipitation of Calcium and Magnesium Ions through Extracellular and Intracellular Process Induced by Bacillus Licheniformis SRB2

“…It has been reported that the decrease of nucleation energy caused by the functional groups on the bacterial surface could induce the mineralization process more easily [48]. Additionally, organic matters secreted by the bacteria played a key role in the regulation of the mineral morphology and phases [45,49,50]. A number of studies have confirmed that some amino acids have an ability to promote the formation of vaterite crystals [51][52][53][54].…”

“…The ion adsorption ability of bacteria is mainly caused by the surface charge and zeta-potential [71]. It has been reported that different functional groups on the surface of bacteria such as hydroxyl, carboxyl, phosphoryl, and amide groups can contribute to this nucleation process [48,49]. In a previous study, it was found that some bacteria can preferentially adsorb Mg 2+ on their membranes to induce the formation of dolomite, and others adsorb Ca 2+ to induce calcite [29].…”