title: Real-Time Manganese Phase Dynamics during Biological and Abiotic Manganese Oxide Reduction.
abstract: Manganese oxides are often highly reactive and easily reduced, both abiotically, by a variety of inorganic chemical species, and biologically during anaerobic respiration by microbes. To evaluate the reaction mechanisms of these different reduction routes and their potential lasting products, we measured the sequence progression of microbial manganese(IV) oxide reduction mediated by chemical species (sulfide and ferrous iron) and the common metal-reducing microbe Shewanella oneidensis MR-1 under several endmember conditions, using synchrotron X-ray spectroscopic measurements complemented by X-ray diffraction and Raman spectroscopy on precipitates collected throughout the reaction. Crystalline or potentially long-lived phases produced in these experiments included manganese(II)-phosphate, manganese(II)-carbonate, and manganese(III)-oxyhydroxides. Major controls on the formation of these discrete phases were alkalinity production and solution conditions such as inorganic carbon and phosphate availability. The formation of a long-lived Mn(III) oxide appears to depend on aqueous Mn(2+) production and the relative proportion of electron donors and electron acceptors in the system. These real-time measurements identify mineralogical products during Mn(IV) oxide reduction, contribute to understanding the mechanism of various Mn(IV) oxide reduction pathways, and assist in interpreting the processes occurring actively in manganese-rich environments and recorded in the geologic record of manganese-rich strata.
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Jena E
authors.initials: JE
authors.lastname: Johnson
authors.affiliation: University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Pratixa
authors.initials: P
authors.lastname: Savalia
authors.affiliation: Stanford Synchrotron Radiation Lightsource , Menlo Park, California 94025, United States.
authors.forename: Ryan
authors.initials: R
authors.lastname: Davis
authors.affiliation: Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Kocar
authors.affiliation: Stanford Synchrotron Radiation Lightsource , Menlo Park, California 94025, United States.
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Webb
authors.affiliation: University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Nealson
authors.affiliation: Division of Geological and Planetary Sciences, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Woodward W
authors.initials: WW
authors.lastname: Fischer
mesh_terms: D001673:Biodegradation, Environmental; D002254:Carbonates / Q000737:chemistry / Q000378:metabolism; D007501:Iron / Q000737:chemistry; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D017895:Manganese Compounds / Q000737:chemistry* / Q000378:metabolism; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry* / Q000378:metabolism; D020592:Shewanella / Q000378:metabolism*; D013059:Spectrum Analysis, Raman; D013440:Sulfides / Q000737:chemistry; D014867:Water / Q000378:metabolism; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D002254:Carbonates; D017895:Manganese Compounds; D009942:Organometallic Compounds; D010087:Oxides; D013440:Sulfides; D014867:Water; D008345:Manganese; C027424:manganese oxide; C045327:manganese carbonate; D007501:Iron; C406182:manganese phosphate