@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 {412,
	title = {Identification of multicomponent histidine-aspartate phosphorelay system controlling flagellar and motility gene expression in Geobacter species.},
	journal = {J Biol Chem},
	volume = {287},
	year = {2012},
	month = {2012 Mar 30},
	pages = {10958-66},
	abstract = {Geobacter species play an important role in the natural biogeochemical cycles of aquatic sediments and subsurface environments as well as in subsurface bioremediation by oxidizing organic compounds with the reduction of insoluble Fe(III) oxides. Flagellum-based motility is considered to be critical for Geobacter species to locate fresh sources of Fe(III) oxides. Functional and comparative genomic approaches, coupled with genetic and biochemical methods, identified key regulators for flagellar gene expression in Geobacter species. A master transcriptional regulator, designated FgrM, is a member of the enhancer-binding protein family. The fgrM gene in the most studied strain of Geobacter species, Geobacter sulfurreducens strain DL-1, is truncated by a transposase gene, preventing flagellar biosynthesis. Integrating a functional FgrM homolog restored flagellar biosynthesis and motility in G. sulfurreducens DL-1 and enhanced the ability to reduce insoluble Fe(III) oxide. Interrupting the fgrM gene in G. sulfurreducens strain KN400, which is motile, removed the capacity for flagellar production and inhibited Fe(III) oxide reduction. FgrM, which is also a response regulator of the two-component His-Asp phosphorelay system, was phosphorylated by histidine kinase GHK4, which was essential for flagellar production and motility. GHK4, which is a hybrid kinase with a receiver domain at the N terminus, was phosphorylated by another histidine kinase, GHK3. Therefore, the multicomponent His-Asp phosphorelay system appears to control flagellar gene expression in Geobacter species.},
	issn = {1083-351X},
	doi = {10.1074/jbc.M112.345041},
	author = {Ueki, Toshiyuki and Leang, Ching and Inoue, Kengo and Lovley, Derek R}
}
@article {404,
	title = {Interspecies electron transfer via hydrogen and formate rather than direct electrical connections in cocultures of Pelobacter carbinolicus and Geobacter sulfurreducens.},
	journal = {Appl Environ Microbiol},
	volume = {78},
	year = {2012},
	month = {2012 Nov},
	pages = {7645-51},
	abstract = {<p>Direct interspecies electron transfer (DIET) is an alternative to interspecies H(2)/formate transfer as a mechanism for microbial species to cooperatively exchange electrons during syntrophic metabolism. To understand what specific properties contribute to DIET, studies were conducted with Pelobacter carbinolicus, a close relative of Geobacter metallireducens, which is capable of DIET. P. carbinolicus grew in coculture with Geobacter sulfurreducens with ethanol as the electron donor and fumarate as the electron acceptor, conditions under which G. sulfurreducens formed direct electrical connections with G. metallireducens. In contrast to the cell aggregation associated with DIET, P. carbinolicus and G. sulfurreducens did not aggregate. Attempts to initiate cocultures with a genetically modified strain of G. sulfurreducens incapable of both H(2) and formate utilization were unsuccessful, whereas cocultures readily grew with mutant strains capable of formate but not H(2) uptake or vice versa. The hydrogenase mutant of G. sulfurreducens compensated, in cocultures, with significantly increased formate dehydrogenase gene expression. In contrast, the transcript abundance of a hydrogenase gene was comparable in cocultures with that for the formate dehydrogenase mutant of G. sulfurreducens or the wild type, suggesting that H(2) was the primary electron carrier in the wild-type cocultures. Cocultures were also initiated with strains of G. sulfurreducens that could not produce pili or OmcS, two essential components for DIET. The finding that P. carbinolicus exchanged electrons with G. sulfurreducens via interspecies transfer of H(2)/formate rather than DIET demonstrates that not all microorganisms that can grow syntrophically are capable of DIET and that closely related microorganisms may use significantly different strategies for interspecies electron exchange.</p>},
	keywords = {Coculture Techniques, Deltaproteobacteria, Electricity, Electron Transport, Electrons, Formates, Geobacter, Hydrogen, Microbial Interactions},
	issn = {1098-5336},
	doi = {10.1128/AEM.01946-12},
	author = {Rotaru, Amelia-Elena and Shrestha, Pravin M and Liu, Fanghua and Ueki, Toshiyuki and Nevin, Kelly and Summers, Zarath M and Lovley, Derek R}
}
