@article {3077,
	title = {Iron Corrosion via Direct Metal-Microbe Electron Transfer.},
	journal = {mBio},
	volume = {10},
	year = {2019},
	month = {2019 May 14},
	abstract = {<p>The concept that anaerobic microorganisms can directly accept electrons from Fe(0) has been controversial because direct metal-microbe electron transfer has previously only been indirectly inferred. Fe(0) oxidation was studied with  strain ACL, an autotrophic strain that was previously shown to grow with electrons derived from a graphite cathode as the sole electron donor. Strain ACL grew with Fe(0) as the sole electron donor and fumarate as the electron acceptor. However, it appeared that at least a portion of the electron transfer was via H produced nonenzymatically from the oxidation of Fe(0) to Fe(II). H, which accumulated in abiotic controls, was consumed during the growth of strain ACL, the cells were predominately planktonic, and genes for the uptake hydrogenase were highly expressed. Strain ACL was constructed to prevent growth on H or formate by deleting the genes for the uptake of hydrogenase and formate dehydrogenases from strain ACL. Strain ACL also grew with Fe(0) as the sole electron donor, but H accumulated in the culture, and cells heavily colonized Fe(0) surfaces with no visible planktonic growth. Transcriptomics suggested that the outer surface -type cytochromes OmcS and OmcZ were important during growth of strain ACL on Fe(0). Strain ACL did not grow on Fe(0) if the gene for either of these cytochromes was deleted. The specific attachment of strain ACL to Fe(0), coupled with requirements for known extracellular electrical contacts, suggest that direct metal-microbe electron transfer is the most likely option for Fe(0) serving as an electron donor. The anaerobic corrosion of iron structures is expensive to repair and can be a safety and environmental concern. It has been known for over 100 years that the presence of anaerobic respiratory microorganisms can accelerate iron corrosion. Multiple studies have suggested that there are sulfate reducers, methanogens, and acetogens that can directly accept electrons from Fe(0) to support sulfate or carbon dioxide reduction. However, all of the strains studied can also use H as an electron donor for growth, which is known to be abiotically produced from Fe(0). Furthermore, no proteins definitely shown to function as extracellular electrical contacts with Fe(0) were identified. The studies described here demonstrate that direct electron transfer from Fe(0) can support anaerobic respiration. They also map out a simple genetic approach to the study of iron corrosion mechanisms in other microorganisms. A better understanding of how microorganisms promote iron corrosion is expected to lead to the development of strategies that can help reduce adverse impacts from this process.</p>},
	keywords = {Anaerobiosis, Corrosion, Cytochromes, Electron Transport, Formate Dehydrogenases, Geobacter, Iron, Oxidation-Reduction, Oxidoreductases, Transcriptome},
	issn = {2150-7511},
	doi = {10.1128/mBio.00303-19},
	author = {Tang, Hai-Yan and Holmes, Dawn E and Ueki, Toshiyuki and Palacios, Paola A and Lovley, Derek R}
}
@article {459,
	title = {Influence of heterogeneous ammonium availability on bacterial community structure and the expression of nitrogen fixation and ammonium transporter genes during in situ bioremediation of uranium-contaminated groundwater.},
	journal = {Environ Sci Technol},
	volume = {43},
	year = {2009},
	month = {2009 Jun 15},
	pages = {4386-92},
	abstract = {The influence of ammonium availability on bacterial community structure and the physiological status of Geobacter species during in situ bioremediation of uranium-contaminated groundwater was evaluated. Ammonium concentrations varied by 2 orders of magnitude (< 4 to 400 microM) across th study site. Analysis of 16S rRNA sequences suggested that ammonium may have been one factor influencing the community composition prior to acetate amendment with Rhodoferax species predominating over Geobacter species with higher ammonium and Dechloromonas species dominating at the site with lowest ammonium. However, once acetate was added and dissimilatory metal reduction was stimulated, Geobacter species became the predominant organisms at all locations. Rates of U(VI) reduction appeared to be more related to acetate concentrations rather than ammonium levels. In situ mRNA transcript abundance of the nitrogen fixation gene, nifD, and the ammonium transporter gene, amtB, in Geobacter species indicated that ammonium was the primary source of nitrogen during uranium reduction. The abundance of amtB was inversely correlated to ammonium levels, whereas nifD transcript levels were similar across all sites examined. These results suggest that nifD and amtB expression are closely regulated in response to ammonium availability to ensure an adequate supply of nitrogen while conserving cell resources. Thus, quantifying nifD and amtB transcript expression appears to be a useful approach for monitoring the nitrogen-related physiological status of subsurface Geobacter species. This study also emphasizes the need for more detailed analysis of geochemical and physiological interactions at the field scale in order to adequately model subsurface microbial processes during bioremediation.},
	keywords = {Carrier Proteins, DNA, Bacterial, Environmental Remediation, Gene Expression Regulation, Bacterial, Gene Library, Geobacter, Nitrogen Fixation, Quaternary Ammonium Compounds, Time Factors, Uranium, Water, Water Pollutants, Radioactive},
	issn = {0013-936X},
	author = {Mouser, Paula J and N{\textquoteright}guessan, Lucie A and Elifantz, Hila and Holmes, Dawn E and Williams, Kenneth H and Wilkins, Michael J and Long, Philip E and Lovley, Derek R}
}
@article {543,
	title = {In situ expression of nifD in Geobacteraceae in subsurface sediments.},
	journal = {Appl Environ Microbiol},
	volume = {70},
	year = {2004},
	month = {2004 Dec},
	pages = {7251-9},
	abstract = {In order to determine whether the metabolic state of Geobacteraceae involved in bioremediation of subsurface sediments might be inferred from levels of mRNA for key genes, in situ expression of nifD, a highly conserved gene involved in nitrogen fixation, was investigated. When Geobacter sulfurreducens was grown without a source of fixed nitrogen in chemostats with acetate provided as the limiting electron donor and Fe(III) as the electron acceptor, levels of nifD transcripts were 4 to 5 orders of magnitude higher than in chemostat cultures provided with ammonium. In contrast, the number of transcripts of recA and the 16S rRNA gene were slightly lower in the absence of ammonium. The addition of acetate to organic- and nitrogen-poor subsurface sediments stimulated the growth of Geobacteraceae and Fe(III) reduction, as well as the expression of nifD in Geobacteraceae. Levels of nifD transcripts in Geobacteraceae decreased more than 100-fold within 2 days after the addition of 100 microM ammonium, while levels of recA and total bacterial 16S rRNA in Geobacteraceae remained relatively constant. Ammonium amendments had no effect on rates of Fe(III) reduction in acetate-amended sediments or toluene degradation in petroleum-contaminated sediments, suggesting that other factors, such as the rate that Geobacteraceae could access Fe(III) oxides, limited Fe(III) reduction. These results demonstrate that it is possible to monitor one aspect of the in situ metabolic state of Geobacteraceae species in subsurface sediments via analysis of mRNA levels, which is the first step toward a more global analysis of in situ gene expression related to nutrient status and stress response during bioremediation by Geobacteraceae.},
	keywords = {Acetates, Biodegradation, Environmental, Culture Media, DNA, Ribosomal, Fresh Water, Gene Expression Regulation, Bacterial, Geobacter, Geologic Sediments, Nitrogenase, Petroleum, Phylogeny, Polymerase Chain Reaction, Quaternary Ammonium Compounds, Rec A Recombinases, RNA, Ribosomal, 16S, Water Pollutants, Chemical},
	issn = {0099-2240},
	doi = {10.1128/AEM.70.12.7251-7259.2004},
	author = {Holmes, Dawn E and Nevin, Kelly P and Lovley, Derek R}
}
