@article {525,
	title = {Genetic characterization of a single bifunctional enzyme for fumarate reduction and succinate oxidation in Geobacter sulfurreducens and engineering of fumarate reduction in Geobacter metallireducens.},
	journal = {J Bacteriol},
	volume = {188},
	year = {2006},
	month = {2006 Jan},
	pages = {450-5},
	abstract = {The mechanism of fumarate reduction in Geobacter sulfurreducens was investigated. The genome contained genes encoding a heterotrimeric fumarate reductase, FrdCAB, with homology to the fumarate reductase of Wolinella succinogenes and the succinate dehydrogenase of Bacillus subtilis. Mutation of the putative catalytic subunit of the enzyme resulted in a strain that lacked fumarate reductase activity and was unable to grow with fumarate as the terminal electron acceptor. The mutant strain also lacked succinate dehydrogenase activity and did not grow with acetate as the electron donor and Fe(III) as the electron acceptor. The mutant strain could grow with acetate as the electron donor and Fe(III) as the electron acceptor if fumarate was provided to alleviate the need for succinate dehydrogenase activity in the tricarboxylic acid cycle. The growth rate of the mutant strain under these conditions was faster and the cell yields were higher than for wild type grown under conditions requiring succinate dehydrogenase activity, suggesting that the succinate dehydrogenase reaction consumes energy. An orthologous frdCAB operon was present in Geobacter metallireducens, which cannot grow with fumarate as the terminal electron acceptor. When a putative dicarboxylic acid transporter from G. sulfurreducens was expressed in G. metallireducens, growth with fumarate as the sole electron acceptor was possible. These results demonstrate that, unlike previously described organisms, G. sulfurreducens and possibly G. metallireducens use the same enzyme for both fumarate reduction and succinate oxidation in vivo.},
	keywords = {Culture Media, Dicarboxylic Acids, Fumarates, Geobacter, Molecular Sequence Data, Operon, Oxidation-Reduction, Recombinant Proteins, Substrate Specificity, Succinate Dehydrogenase, Succinic Acid},
	issn = {0021-9193},
	doi = {10.1128/JB.188.2.450-455.2006},
	author = {Butler, Jessica E and Glaven, Richard H and Esteve-N{\'u}{\~n}ez, Abraham and N{\'u}{\~n}ez, Cinthia and Shelobolina, Evgenya S and Bond, Daniel R and Lovley, Derek R}
}
@article {533,
	title = {Characterization of citrate synthase from Geobacter sulfurreducens and evidence for a family of citrate synthases similar to those of eukaryotes throughout the Geobacteraceae.},
	journal = {Appl Environ Microbiol},
	volume = {71},
	year = {2005},
	month = {2005 Jul},
	pages = {3858-65},
	abstract = {Members of the family Geobacteraceae are commonly the predominant Fe(III)-reducing microorganisms in sedimentary environments, as well as on the surface of energy-harvesting electrodes, and are able to effectively couple the oxidation of acetate to the reduction of external electron acceptors. Citrate synthase activity of these organisms is of interest due to its key role in acetate metabolism. Prior sequencing of the genome of Geobacter sulfurreducens revealed a putative citrate synthase sequence related to the citrate synthases of eukaryotes. All citrate synthase activity in G. sulfurreducens could be resolved to a single 49-kDa protein via affinity chromatography. The enzyme was successfully expressed at high levels in Escherichia coli with similar properties as the native enzyme, and kinetic parameters were comparable to related citrate synthases (kcat= 8.3 s(-1); Km= 14.1 and 4.3 microM for acetyl coenzyme A and oxaloacetate, respectively). The enzyme was dimeric and was slightly inhibited by ATP (Ki= 1.9 mM for acetyl coenzyme A), which is a known inhibitor for many eukaryotic, dimeric citrate synthases. NADH, an allosteric inhibitor of prokaryotic hexameric citrate synthases, did not affect enzyme activity. Unlike most prokaryotic dimeric citrate synthases, the enzyme did not have any methylcitrate synthase activity. A unique feature of the enzyme, in contrast to citrate synthases from both eukaryotes and prokaryotes, was a lack of stimulation by K+ ions. Similar citrate synthase sequences were detected in a diversity of other Geobacteraceae members. This first characterization of a eukaryotic-like citrate synthase from a prokaryote provides new insight into acetate metabolism in Geobacteraceae members and suggests a molecular target for tracking the presence and activity of these organisms in the environment.},
	keywords = {Amino Acid Sequence, Citrate (si)-Synthase, Culture Media, Deltaproteobacteria, DNA, Bacterial, Eukaryotic Cells, Geobacter, Kinetics, Molecular Sequence Data, Phylogeny, Sequence Analysis, DNA},
	issn = {0099-2240},
	doi = {10.1128/AEM.71.7.3858-3865.2005},
	author = {Bond, Daniel R and Mester, T{\"u}nde and Nesb{\o}, Camilla L and Izquierdo-Lopez, Andrea V and Collart, Frank L and Lovley, Derek R}
}
@article {552,
	title = {Graphite electrodes as electron donors for anaerobic respiration.},
	journal = {Environ Microbiol},
	volume = {6},
	year = {2004},
	month = {2004 Jun},
	pages = {596-604},
	abstract = {It has been demonstrated previously that Geobacter species can transfer electrons directly to electrodes. In order to determine whether electrodes could serve as electron donors for microbial respiration, enrichment cultures were established from a sediment inoculum with a potentiostat-poised graphite electrode as the sole electron donor and nitrate as the electron acceptor. Nitrate was reduced to nitrite with the consumption of electrical current. The stoichiometry of electron and nitrate consumption and nitrite accumulation were consistent with the electrode serving as the sole electron donor for nitrate reduction. Analysis of 16 rRNA gene sequences demonstrated that the electrodes supplied with current were specifically enriched in microorganisms with sequences most closely related to the sequences of known Geobacter species. A pure culture of Geobacter metallireducens was shown to reduce nitrate to nitrite with the electrode as the sole electron donor with the expected stoichiometry of electron consumption. Cells attached to the electrode appeared to be responsible for the nitrate reduction. Attached cells of Geobacter sulfurreducens reduced fumarate to succinate with the electrode as an electron donor. These results demonstrate for the first time that electrodes may serve as a direct electron donor for anaerobic respiration. This finding has implications for the harvesting of electricity from anaerobic sediments and the bioremediation of oxidized contaminants.},
	keywords = {Anaerobiosis, Electrodes, Electrons, Fumarates, Geobacter, Geologic Sediments, Graphite, Kinetics, Microscopy, Electron, Scanning, Nitrates, Phylogeny, RNA, Ribosomal, 16S, Sequence Analysis, DNA},
	issn = {1462-2912},
	doi = {10.1111/j.1462-2920.2004.00593.x},
	author = {Gregory, Kelvin B and Bond, Daniel R and Lovley, Derek R}
}
