In order to simulate bio-reduction of manganese oxides and coupled carbonate precipitation induced by microbes in shallow sea environments, we took one of the most common manganese oxides-birnessite (K0.33Mn7O14~7H2O) as an example and carried out experiments under different Mg2+ and SO42- concentrations, where dissimilatory manganese-reducing bacteria Dietzia cercidiphylli 45-1b reduced birnessite under aerobic conditions. By analyzing variations of the concentrations of protein, Mn2+, etc., alongside X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) for mineralogical transformations analyses, we discussed the impact on birnessite reduction and carbonate precipitation by Strain 45-1b under different initial concentrations of Mg2+ and SO42-. Results show that the pH in our experimental systems quickly increased from 7.0 to 9.3 during the course of four days, and Mn2+ concentrations increased to 166 mol/L in two days and rapidly decreased to 8 mol/L on the fourth day with rhodochrosite (MnCO3) as reduction products under aerobic conditions.The production of rhodochrosite decreased with increasing Mg2+ concentrations and increased with rising SO42- concentrations. These results indicate that Strain 45-1b can utilize acetate as the electron donor and birnessite as the electron acceptor under aerobic conditions, causing birnessite reduction and Mn2+ releasing and ultimately conversing organic carbon into inorganic carbonate minerals as rhodochrosite. Mg2+ inhibited microbial growth and the presence of rhodochrosite nucleation sites to affect birnessite reduction and rhodochrosite precipitation, and SO42- mitigated Mg2+ inhibition and promoted birnessite reduction and rhodochrosite~precipitation.
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