@article {3074,
	title = {A Membrane-Bound Cytochrome Enables  To Conserve Energy from Extracellular Electron Transfer.},
	journal = {mBio},
	volume = {10},
	year = {2019},
	month = {2019 Aug 20},
	abstract = {<p>Extracellular electron exchange in  species and closely related  plays an important role in the global carbon cycle and enhances the speed and stability of anaerobic digestion by facilitating efficient syntrophic interactions. Here, we grew  with methanol provided as the electron donor and the humic analogue, anthraquione-2,6-disulfonate (AQDS), provided as the electron acceptor when methane production was inhibited with bromoethanesulfonate. AQDS was reduced with simultaneous methane production in the absence of bromoethanesulfonate. Transcriptomics revealed that expression of the gene for the transmembrane, multiheme, -type cytochrome MmcA was higher in AQDS-respiring cells than in cells performing methylotrophic methanogenesis. A strain in which the gene for MmcA was deleted failed to grow via AQDS reduction but grew with the conversion of methanol or acetate to methane, suggesting that MmcA has a specialized role as a conduit for extracellular electron transfer. Enhanced expression of genes for methanol conversion to methyl-coenzyme M and the Rnf complex suggested that methanol is oxidized to carbon dioxide in AQDS-respiring cells through a pathway that is similar to methyl-coenzyme M oxidation in methanogenic cells. However, during AQDS respiration the Rnf complex and reduced methanophenazine probably transfer electrons to MmcA, which functions as the terminal reductase for AQDS reduction. Extracellular electron transfer may enable the survival of methanogens in dynamic environments in which oxidized humic substances and Fe(III) oxides are intermittently available. The availability of tools for genetic manipulation of  makes it an excellent model microbe for evaluating -type cytochrome-dependent extracellular electron transfer in  The discovery of a methanogen that can conserve energy to support growth solely from the oxidation of organic carbon coupled to the reduction of an extracellular electron acceptor expands the possible environments in which methanogens might thrive. The potential importance of -type cytochromes for extracellular electron transfer to syntrophic bacterial partners and/or Fe(III) minerals in some  was previously proposed, but these studies with  provide the first genetic evidence for cytochrome-based extracellular electron transfer in  The results suggest parallels with Gram-negative bacteria, such as  and  species, in which multiheme outer-surface -type cytochromes are an essential component for electrical communication with the extracellular environment.  offers an unprecedented opportunity to study mechanisms for energy conservation from the anaerobic oxidation of one-carbon organic compounds coupled to extracellular electron transfer in  with implications not only for methanogens but possibly also for  that anaerobically oxidize methane.</p>},
	keywords = {Acetates, Anthraquinones, Cytochromes, Electron Transport, Electrons, Ferric Compounds, Gene Expression Regulation, Archaeal, Gram-Negative Bacteria, Membranes, Mesna, Methane, Methanol, Methanosarcina, Oxidation-Reduction, Oxidoreductases, Transcriptome},
	issn = {2150-7511},
	doi = {10.1128/mBio.00789-19},
	author = {Holmes, Dawn E and Ueki, Toshiyuki and Tang, Hai-Yan and Zhou, Jinjie and Smith, Jessica A and Chaput, Gina and Lovley, Derek R}
}
@article {3154,
	title = {Characterization and transcription of arsenic respiration and resistance genes during in situ uranium bioremediation.},
	journal = {ISME J},
	volume = {7},
	year = {2013},
	month = {2013 Feb},
	pages = {370-83},
	abstract = {<p>The possibility of arsenic release and the potential role of Geobacter in arsenic biogeochemistry during in situ uranium bioremediation was investigated because increased availability of organic matter has been associated with substantial releases of arsenic in other subsurface environments. In a field experiment conducted at the Rifle, CO study site, groundwater arsenic concentrations increased when acetate was added. The number of transcripts from arrA, which codes for the α-subunit of dissimilatory As(V) reductase, and acr3, which codes for the arsenic pump protein Acr3, were determined with quantitative reverse transcription-PCR. Most of the arrA (>60\%) and acr3-1 (>90\%) sequences that were recovered were most similar to Geobacter species, while the majority of acr3-2 (>50\%) sequences were most closely related to Rhodoferax ferrireducens. Analysis of transcript abundance demonstrated that transcription of acr3-1 by the subsurface Geobacter community was correlated with arsenic concentrations in the groundwater. In contrast, Geobacter arrA transcript numbers lagged behind the major arsenic release and remained high even after arsenic concentrations declined. This suggested that factors other than As(V) availability regulated the transcription of arrA in situ, even though the presence of As(V) increased the transcription of arrA in cultures of Geobacter lovleyi, which was capable of As(V) reduction. These results demonstrate that subsurface Geobacter species can tightly regulate their physiological response to changes in groundwater arsenic concentrations. The transcriptomic approach developed here should be useful for the study of a diversity of other environments in which Geobacter species are considered to have an important influence on arsenic biogeochemistry.</p>},
	keywords = {Acetates, Arsenate Reductases, Arsenic, Biodegradation, Environmental, Colorado, Gene Expression Regulation, Bacterial, Genes, Bacterial, Geobacter, Groundwater, Transcriptome, Uranium},
	issn = {1751-7370},
	doi = {10.1038/ismej.2012.109},
	author = {Giloteaux, Ludovic and Holmes, Dawn E and Williams, Kenneth H and Wrighton, Kelly C and Wilkins, Michael J and Montgomery, Alison P and Smith, Jessica A and Orellana, Roberto and Thompson, Courtney A and Roper, Thomas J and Long, Philip E and Lovley, Derek R}
}
