Biomineralization of Carbonate Minerals Induced by The Moderate Halophile Staphylococcus Warneri YXY2

Abstract

Although biomineralization of minerals induced by microorganisms has been widely reported, the mechanisms of biomineralization and the characteristics of the biominerals precipitated needs to be studied further. In this study, Staphylococcus warneri YXY2, a moderate halophile, was used to induce the precipitation of carbonate minerals at various Mg/Ca molar ratios. To investigate the biomineralization mechanism, the growth curve, pH changes, ammonia test, the concentration of bicarbonate and carbonate ions, and the activity of carbonic anhydrase (CA) and alkaline phosphatase (ALP) were determined. X-ray powder diffraction (XRD), scanning electron microscopy - energy disperse spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and stable carbon isotope analyses were used to characterize the minerals. The obtained biotic minerals were calcite, vaterite, Mg-rich calcite, and aragonite crystals. The crystallinity of aragonite decreased with increasing Mg/Ca ratios. The preferred orientation, diverse morphologies, organic substances, and more negative stable carbon isotope values proved the biogenesis of these carbonate minerals. The presence of Mg in the biotic aragonite crystals was likely related to the acidic amino acids which also facilitated the nucleation of minerals on/in the extracellular polymeric substances (EPS). Mg2+ and Ca2+ ions were able to enter into the YXY2 bacteria to induce intracellular biomineralization. Dynamics simulation using Material Studio software proved that different adsorption energies of Glutamic acid (Glu) adsorbed onto different crystal planes of aragonite led to the preferred orientation of aragonite. This study helps to deepen our understanding of biomineralization mechanisms and may be helpful to distinguish biotic minerals from abiotic minerals.