@article {427,
	title = {Biochemical characterization of purified OmcS, a c-type cytochrome required for insoluble Fe(III) reduction in Geobacter sulfurreducens.},
	journal = {Biochim Biophys Acta},
	volume = {1807},
	year = {2011},
	month = {2011 Apr},
	pages = {404-12},
	abstract = {Previous studies with Geobacter sulfurreducens have demonstrated that OmcS, an abundant c-type cytochrome that is only loosely bound to the outer surface, plays an important role in electron transfer to Fe(III) oxides as well as other extracellular electron acceptors. In order to further investigate the function of OmcS, it was purified from a strain that overproduces the protein. Purified OmcS had a molecular mass of 47015 Da, and six low-spin bis-histidinyl hexacoordinated heme groups. Its midpoint redox potential was -212 mV. A thermal stability analysis showed that the cooperative melting of purified OmcS occurs in the range of 65-82 {\textdegree}C. Far UV circular dichroism spectroscopy indicated that the secondary structure of purified OmcS consists of about 10\% α-helix and abundant disordered structures. Dithionite-reduced OmcS was able to transfer electrons to a variety of substrates of environmental importance including insoluble Fe(III) oxide, Mn(IV) oxide and humic substances. Stopped flow analysis revealed that the reaction rate of OmcS oxidation has a hyperbolic dependence on the concentration of the studied substrates. A ten-fold faster reaction rate with anthraquinone-2,6-disulfonate (AQDS) (25.2 s$^{-}${\textonesuperior}) was observed as compared to that with Fe(III) citrate (2.9 s$^{-}${\textonesuperior}). The results, coupled with previous localization and gene deletion studies, suggest that OmcS is well-suited to play an important role in extracellular electron transfer.},
	keywords = {Circular Dichroism, Cytochrome c Group, Geobacter, Heme, Iron, Kinetics, Molecular Weight, Oxidation-Reduction, Solubility},
	issn = {0006-3002},
	doi = {10.1016/j.bbabio.2011.01.003},
	author = {Qian, Xinlei and Mester, T{\"u}nde and Morgado, Leonor and Arakawa, Tsutomu and Sharma, Manju L and Inoue, Kengo and Joseph, Crisjoe and Salgueiro, Carlos A and Maroney, Michael J and Lovley, Derek R}
}
@article {454,
	title = {Modeling and sensitivity analysis of electron capacitance for Geobacter in sedimentary environments.},
	journal = {J Contam Hydrol},
	volume = {112},
	year = {2010},
	month = {2010 Mar 1},
	pages = {30-44},
	abstract = {In situ stimulation of the metabolic activity of Geobacter species through acetate amendment has been shown to be a promising bioremediation strategy to reduce and immobilize hexavalent uranium [U(VI)] as insoluble U(IV). Although Geobacter species are reducing U(VI), they primarily grow via Fe(III) reduction. Unfortunately, the biogeochemistry and the physiology of simultaneous reduction of multiple metals are still poorly understood. A detailed model is therefore required to better understand the pathways leading to U(VI) and Fe(III) reduction by Geobacter species. Based on recent experimental evidence of temporary electron capacitors in Geobacter we propose a novel kinetic model that physically distinguishes planktonic cells into electron-loaded and -unloaded states. Incorporation of an electron load-unload cycle into the model provides insight into U(VI) reduction efficiency, and elucidates the relationship between U(VI)- and Fe(III)-reducing activity and further explains the correlation of high U(VI) removal with high fractions of planktonic cells in subsurface environments. Global sensitivity analysis was used to determine the level of importance of geochemical and microbial processes controlling Geobacter growth and U(VI) reduction, suggesting that the electron load-unload cycle and the resulting repartition of the microbes between aqueous and attached phases are critical for U(VI) reduction. As compared with conventional Monod modeling approaches without inclusion of the electron capacitance, the new model attempts to incorporate a novel cellular mechanism that has a significant impact on the outcome of in situ bioremediation.},
	keywords = {Biodegradation, Environmental, Electric Capacitance, Geobacter, Kinetics, Models, Biological, Uranium},
	issn = {1873-6009},
	doi = {10.1016/j.jconhyd.2009.10.002},
	author = {Zhao, Jiao and Fang, Yilin and Scheibe, Timothy D and Lovley, Derek R and Mahadevan, R}
}
@article {523,
	title = {Harvesting energy from the marine sediment-water interface II. Kinetic activity of anode materials.},
	journal = {Biosens Bioelectron},
	volume = {21},
	year = {2006},
	month = {2006 May 15},
	pages = {2058-63},
	abstract = {Here, we report a comparative study on the kinetic activity of various anodes of a recently described microbial fuel cell consisting of an anode imbedded in marine sediment and a cathode in overlying seawater. Using plain graphite anodes, it was demonstrated that a significant portion of the anodic current results from oxidation of sediment organic matter catalyzed by microorganisms colonizing the anode and capable of directly reducing the anode without added exogenous electron-transfer mediators. Here, graphite anodes incorporating microbial oxidants are evaluated in the laboratory relative to plain graphite with the goal of increasing power density by increasing current density. Anodes evaluated include graphite modified by adsorption of anthraquinone-1,6-disulfonic acid (AQDS) or 1,4-naphthoquinone (NQ), a graphite-ceramic composite containing Mn2+ and Ni2+, and graphite modified with a graphite paste containing Fe3O4 or Fe3O4 and Ni2+. It was found that these anodes possess between 1.5- and 2.2-fold greater kinetic activity than plain graphite. Fuel cells were deployed in a coastal site near Tuckerton, NJ (USA) that utilized two of these anodes. These fuel cells generated ca. 5-fold greater current density than a previously characterized fuel cell equipped with a plain graphite anode, and operated at the same site.},
	keywords = {Electrochemistry, Electrodes, Energy-Generating Resources, Ferumoxytol, Geologic Sediments, Kinetics, Oceans and Seas, Seawater},
	issn = {0956-5663},
	doi = {10.1016/j.bios.2006.01.033},
	author = {Lowy, Daniel A and Tender, Leonard M and Zeikus, J Gregory and Park, Doo Hyun 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 {548,
	title = {Direct correlation between rates of anaerobic respiration and levels of mRNA for key respiratory genes in Geobacter sulfurreducens.},
	journal = {Appl Environ Microbiol},
	volume = {70},
	year = {2004},
	month = {2004 Sep},
	pages = {5183-9},
	abstract = {The predominance of Geobacter species in environments in which Fe(III) reduction is important has suggested that Fe(III) reduction rates might be estimated in Geobacter-dominated environments by assessing in situ activity with molecular techniques. To determine whether mRNA levels of key respiratory genes might be correlated with respiration rates in Geobacter sulfurreducens, studies were conducted with fumarate as the electron acceptor and acetate as the limiting electron donor in anaerobic continuous cultures. Levels of mRNA for a fumarate reductase gene, frdA, quantified by real-time reverse transcription-PCR were directly correlated with fumarate reduction rates. In similar studies with Fe(III) as the electron acceptor, mRNA levels for omcB, a gene for an outer membrane c-type cytochrome involved in Fe(III) reduction, were positively correlated with Fe(III) reduction rates. Levels of mRNA for frdA and omcB were also positively correlated with fumarate and Fe(III) reduction rates, respectively, when growth was limited by the availability of fumarate or Fe(III), but mRNA levels were higher than in acetate-limited cultures. Levels of mRNA for omcC, which encodes a c-type cytochrome highly similar to OmcB but not necessary for Fe(III) reduction, followed patterns different than those of omcB. This agrees with the previous finding that OmcC is not involved in Fe(III) reduction and suggests that changes in mRNA levels of omcB are related to its role in Fe(III) reduction. These results demonstrate that mRNA levels for respiratory genes might be used to estimate in situ Fe(III) reduction rates in Geobacter-dominated environments but suggest that information on environmental conditions and/or the metabolic state of Geobacter species is also required for accurate rate estimates.},
	keywords = {Anaerobiosis, Base Sequence, DNA Primers, Geobacter, Kinetics, Oxygen Consumption, Polymerase Chain Reaction, RNA, Messenger},
	issn = {0099-2240},
	doi = {10.1128/AEM.70.9.5183-5189.2004},
	author = {Chin, Kuk-Jeong and Esteve-N{\'u}{\~n}ez, Abraham and Leang, Ching 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}
}
