In situ characterization of Mn(II) oxidation by spores of the marine Bacillus sp. strain SG-1

Microbial oxidation of Mn(II) and subsequent precipitation of insoluble, reactive Mn(IV) oxides are primary sources of these solid phases in the environment and key controls on Mn cycling in natural waters. We have performed in situ x-ray absorption near-edge structure (XANES) spectroscopic measurements of Mn(II) oxidation by spores of the marine Bacillus sp. strain SG-1 to characterize the intermediates and products of the oxidation reactions. Mn(IV)-oxides resembling δ-MnO2 were observed to form at a rapid rate (within 14 min of reaction onset). Mn(III) intermediates did not occur above detection limit (5 to 10% of total Mn), even though Mn(III)/(II,III) oxides (MnOOH or Mn3O4) should have been more stable than MnO2 under the conditions of the experiments. These results suggest that Mn(IV) is the primary product of bacterial Mn(II) oxidation by Bacillus strain SG-1. Given that SG-1 is a good model for Mn(II)-oxidizing bacteria, these findings help to explain the predominance of Mn(IV)-oxides in aquatic environments.