Chapter 9 : Anaerobic Respiratory Iron(II) Oxidation

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This chapter explores what is known about anaerobic, mesophilic Fe(II) oxidation in environmental samples and pure cultures. It includes an investigation of the mechanism of Fe(II) oxidation by dissimilatory (per)chlorate-reducing bacteria (DPRB), and a discussion on the oxidation products formed by the biomineralization processes, and emerging applications for the metabolism. Isolation and study of pure cultures have provided the needed starting points for investigating the presence of organisms in environmental samples and examining the microbial ecology of nitrate-dependent Fe(II) oxidation. The selective anaerobic bio-oxidation of added Fe(II) in situ could be used as an effective means of “capping off ” and completing the attenuation of heavy metals and radionuclides in a reducing environment. Two recent studies have also demonstrated the ability of both pure and mixed cultures to successfully adsorb arsenic to iron(III) oxides generated during this process. Genome sequences of several known nitrate-dependent Fe(II)-oxidizing microorganisms (FOM) are now available or in the process of completion, and comparative genomics should yield potential targets for further genetic study of the metabolism. The variety of culture-independent techniques now in use for assessment of microbial ecology will inevitably lead to a better understanding of the prevalence, biogeography, and diversity of FOM in natural and contaminated settings. The combined efforts of types of studies will help develop more accurate models regarding the role of FOM in the biogeochemical cycling of nitrogen, iron, and carbon.

Citation: Cameron Thrash J, Ahmadi S, Coates J. 2011. Anaerobic Respiratory Iron(II) Oxidation, p 157-171. In Stolz J, Oremland R (ed), Microbial Metal and Metalloid Metabolism. ASM Press, Washington, DC. doi: 10.1128/9781555817190.ch9
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The microbially mediated iron redox cycle. Over the past two decades it has been unambiguously demonstrated that microorganisms play a central role in the environmental geochemical redox cycle of iron. Microbial Fe(III) reduction is mediated primarily through the activity of dissimilatory metal-reducing bacteria under anaerobic conditions, while Fe(II) oxidation can occur through the activity of both photolithotrophic Fe(II) oxidizers using Fe(II) as an electron source for CO reduction, or chemolithotrophic respiratory Fe(II)-oxidizing bacteria (aerobic and anaerobic) using Fe(II) as an energy and electron source for carbon assimilation with a variety of alternative electron acceptors. Both Fe(III)-reducing and Fe(II)-oxidizing microorganisms have been shown to use either soluble or solid-phase iron sources, thus extending the biogeochemical cycle of iron to beyond the soluble form. 10.1128/9781555817190.ch9.f1

Citation: Cameron Thrash J, Ahmadi S, Coates J. 2011. Anaerobic Respiratory Iron(II) Oxidation, p 157-171. In Stolz J, Oremland R (ed), Microbial Metal and Metalloid Metabolism. ASM Press, Washington, DC. doi: 10.1128/9781555817190.ch9
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Phylogenetic diversity of anaerobic Fe(II)-oxidizing microorganisms. Available quality 16S rRNA gene sequences were aligned with MUSCLE ( ) and phylogeny was computed with MrBayes 3.2 ( ). Scale bar indicates 0.2 changes per position. 10.1128/9781555817190.ch9.f2

Citation: Cameron Thrash J, Ahmadi S, Coates J. 2011. Anaerobic Respiratory Iron(II) Oxidation, p 157-171. In Stolz J, Oremland R (ed), Microbial Metal and Metalloid Metabolism. ASM Press, Washington, DC. doi: 10.1128/9781555817190.ch9
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Effect of Fe(II) and Fe(III) on heterotrophic growth of strain VDY. ■, cells with added Fe(II); ●, cells with added Fe(III); ○, cells with no added iron; ▲, (ClO ) for cells with added Fe(II); ◆, (ClO ) for cells with added Fe(III); ☐, (ClO ) for cells with no added iron. 10.1128/9781555817190.ch9.f3

Citation: Cameron Thrash J, Ahmadi S, Coates J. 2011. Anaerobic Respiratory Iron(II) Oxidation, p 157-171. In Stolz J, Oremland R (ed), Microbial Metal and Metalloid Metabolism. ASM Press, Washington, DC. doi: 10.1128/9781555817190.ch9
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Model for possible iterations of iron with the perchlorate-reduction pathway of strain VDY. Both Fe(II) and Fe(III) are postulated to inhibit chlorite dismutase (Cld). This prevents the formation and subsequent reduction of oxygen, disabling the creation of a proton motive force. Cld inhibition would also cause a buildup of chlorite, which is toxic to the cell and can also abiotically react with iron(II). OM, outer membrane; PM, periplasmic membrane; Pcr, perchlorate reductase. 10.1128/9781555817190.ch9.f4

Citation: Cameron Thrash J, Ahmadi S, Coates J. 2011. Anaerobic Respiratory Iron(II) Oxidation, p 157-171. In Stolz J, Oremland R (ed), Microbial Metal and Metalloid Metabolism. ASM Press, Washington, DC. doi: 10.1128/9781555817190.ch9
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