S. M. Webb,1 B. M. Tebo,2 J. R. Bargar1
2Scripps Institute of Oceanography, Marine Biology Research Division
Natural Mn oxide colloids and grain coatings are ubiquitous in the environment and profoundly impact the ground water quality via their ability to degrade and sequester contaminants. These oxides are dominantly generated via bacterial oxidation of Mn(II) and have extremely high sorptive capacities for heavy metals. In addition, Mn oxides readily oxidize a variety of recalcitrant organic and inorganic compounds. The mechanis(s) and products of bacterial Mn(II) oxidation are therefore believed to have deep and wide-ranging roles in the environmental cycling of trace metals, organics, and carbon.
We have utilized XAS and synchrotron-based in-situ transmission XRD to
the structures of fully hydrated biogenic Mn oxides produced by spores of the
marine bacterium, Bacillus sp., strain SG-1. Biooxides were produced
absence and presence of Co(II), which has a high affinity for Mn oxides and can
oxidize to Mn(III). The primary biogenic reaction product is a poorly
crystalline solid similar to
which Mn has an oxidation state close
to 4+. The structure of the oxide is analogous to acid birnessite, but with
fewer layer vacancies and greater local order around Mn(IV). Co(II) is
oxidized to Co(III) and incorporated at Mn(IV) sites in the octahedral layer.
The presence of Co(III) alters the stability and structure of the host Mn
oxides. This observation, combined with the very high sorptive capacity of the
Mn oxides, imply that bacteria can exert tremendous influence over Co cycling
in impacted waters via Mn oxide biomineralization.