Abstract
The bioreduction of Fe(III) oxides by dissimilatory iron reducing bacteria (DIRB) may result in the production of a suite of Fe(II)-bearing secondary minerals, including magnetite, siderite, vivianite, green rusts, and chukanovite; the formation of specific phases controlled by the interaction of various physiological and geochemical factors. In an effort to better understand the effects of individual electron donors on the formation of specific Fe(II)-bearing secondary minerals, we examined the effects of a series of potential electron donors on the bioreduction of lepidocrocite (γ-FeOOH) by Shewanella putrefaciens CN32. Biomineralization products were identified by X-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy. Acetate, citrate, ethanol, glucose, glutamate, glycerol, malate, and succinate were not effectively utilized for the bioreduction of lepidocrocite by S. putrefaciens CN32; however, substantial Fe(II) production was observed when formate, lactate, H2, pyruvate, serine, or N acetylglucosamine (NAG) was provided as an electron donor. Carbonate or sulfate green rust was the dominant Fe(II)-bearing secondary mineral when formate, H2, lactate, or NAG was provided, however, siderite formed with pyruvate or serine. Geochemical modeling indicated that pH and carbonate concentration are the key factors determining the prevalence of carbonate green rust verses siderite.
Highlights
Iron (Fe) is a highly abundant element in the lithosphere
In this study we examine the ability of Shewanella putrefaciens CN32 to utilize a broad range of potential electron donors for anaerobic respiration using Fe(III) oxide as an electron acceptor for anaerobic respiration
Formate essentially served as a positive control given that we have previously shown that formate is utilized as an electron donor for dissimilatory iron-reducing (DIR) by S. putrefaciens CN32 [16,28,44,55,63]
Summary
Iron (Fe) is a highly abundant element in the lithosphere. Fe-bearing clay minerals (smectites, illites, chlorites, etc.) and Fe oxides (including formal Fe oxides, oxyhydroxides, and hydroxides such as ferrihydrite, hematite (α-Fe2 O3 ), maghemite (γ-Fe2 O3 ), magnetite (Fe3 O4 ), goethite (α-FeOOH), and lepidocrocite (γ-FeOOH)) are common constituents of soils and sediments. The presence of Fe(II) in suboxic to anoxic near surface environments is typically the result of the activity of dissimilatory iron-reducing (DIR) bacteria and archaea. These phylogenetically diverse microorganisms can couple the oxidation of organic compounds or hydrogen (H2 ) to the reduction of Fe(III) to Fe(II) [6,7,8,9,10,11,12,13,14,15,16,17,18,19]. Dissimilatory iron-reducing bacteria (DIRB) are able to use soluble Fe(III) complexes (e.g., ferric citrate), Fe(III) oxides, and Fe(III)-bearing clay minerals as terminal electron acceptors for anaerobic respiration [20,21,22,23,24,25,26,27,28]
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