@article {3054, title = {Electrotrophy: Other microbial species, iron, and electrodes as electron donors for microbial respirations.}, journal = {Bioresour Technol}, volume = {345}, year = {2022}, month = {2022 Feb}, pages = {126553}, abstract = {

Electrotrophy, the growth of microbes on extracellular electron donors, drives important biogeochemical cycles and has practical applications. Studies of Fe(II)-based electrotrophy have provided foundational cytochrome-based mechanistic models for electron transport into cells. Direct electron uptake from other microbial species, Fe(0), or cathodes is of intense interest due to its potential roles in the production and anaerobic oxidation of methane, corrosion, and bioelectrochemical technologies. Other cells or Fe(0) can serve as the sole electron donor supporting the growth of several Geobacter and methanogen strains that are unable to use H as an electron donor, providing strong evidence for electrotrophy. Additional evidence for electrotrophy in Geobacter strains and Methanosarcina acetivorans is a requirement for outer-surface c-type cytochromes. However, in most instances claims for electrotrophy in anaerobes are based on indirect inference and the possibility that H is actually the electron donor supporting growth has not been rigorously excluded.

}, keywords = {Electrodes, Electron Transport, Electrons, Geobacter, Iron, Oxidation-Reduction, Soil Microbiology}, issn = {1873-2976}, doi = {10.1016/j.biortech.2021.126553}, author = {Lovley, Derek R} } @article {3048, title = {Microbial biofilms for electricity generation from water evaporation and power to wearables.}, journal = {Nat Commun}, volume = {13}, year = {2022}, month = {2022 Jul 28}, pages = {4369}, abstract = {

Employing renewable materials for fabricating clean energy harvesting devices can further improve sustainability. Microorganisms can be mass produced with renewable feedstocks. Here, we demonstrate that it is possible to engineer microbial biofilms as a cohesive, flexible material for long-term continuous electricity production from evaporating water. Single biofilm sheet (~40 {\textmu}m thick) serving as the functional component in an electronic device continuously produces power density (~1 μW/cm) higher than that achieved with thicker engineered materials. The energy output is comparable to that achieved with similar sized biofilms catalyzing current production in microbial fuel cells, without the need for an organic feedstock or maintaining cell viability. The biofilm can be sandwiched between a pair of mesh electrodes for scalable device integration and current production. The devices maintain the energy production in ionic solutions and can be used as skin-patch devices to harvest electricity from sweat and moisture on skin to continuously power wearable devices. Biofilms made from different microbial species show generic current production from water evaporation. These results suggest that we can harness the ubiquity of biofilms in nature as additional sources of biomaterial for evaporation-based electricity generation in diverse aqueous environments.

}, keywords = {Bioelectric Energy Sources, Biofilms, Electricity, Electrodes, Water, Wearable Electronic Devices}, issn = {2041-1723}, doi = {10.1038/s41467-022-32105-6}, author = {Liu, Xiaomeng and Ueki, Toshiyuki and Gao, Hongyan and Woodard, Trevor L and Nevin, Kelly P and Fu, Tianda and Fu, Shuai and Sun, Lu and Lovley, Derek R and Yao, Jun} } @article {3094, title = {Expressing the Geobacter metallireducens PilA in Geobacter sulfurreducens Yields Pili with Exceptional Conductivity.}, journal = {mBio}, volume = {8}, year = {2017}, month = {2017 Jan 17}, abstract = {

UNLABELLED: The electrically conductive pili (e-pili) of Geobacter sulfurreducens serve as a model for a novel strategy for long-range extracellular electron transfer. e-pili are also a new class of bioelectronic materials. However, the only other Geobacter pili previously studied, which were from G.~uraniireducens, were poorly conductive. In order to obtain more information on the range of pili conductivities in Geobacter species, the pili of G.~metallireducens were investigated. Heterologously expressing the PilA gene of G.~metallireducens in G.~sulfurreducens yielded a G.~sulfurreducens strain, designated strain MP, that produced abundant pili. Strain MP exhibited phenotypes consistent with the presence of e-pili, such as high rates of Fe(III) oxide reduction and high current densities on graphite anodes. Individual pili prepared at physiologically relevant pH~7 had conductivities of 277 {\textpm} 18.9 S/cm (mean {\textpm} standard deviation), which is 5,000-fold higher than the conductivity of G.~sulfurreducens pili at pH~7 and nearly 1 million-fold higher than the conductivity of G.~uraniireducens pili at the same pH. A potential explanation for the higher conductivity of the G.~metallireducens pili is their greater density of aromatic amino acids, which are known to be important components in electron transport along the length of the pilus. The G.~metallireducens pili represent the most highly conductive pili found to date and suggest strategies for designing synthetic pili with even higher conductivities.

IMPORTANCE: e-pili are a remarkable electrically conductive material that can be sustainably produced without harsh chemical processes from renewable feedstocks and that contain no toxic components in the final product. Thus, e-pili offer an unprecedented potential for developing novel materials, electronic devices, and sensors for diverse applications with a new "green" technology. Increasing e-pili conductivity will even further expand their potential applications. A proven strategy is to design synthetic e-pili that contain tryptophan, an aromatic amino acid not found in previously studied e-pili. The studies reported here demonstrate that a productive alternative approach is to search more broadly in the microbial world. Surprisingly, even though G.~metallireducens and G.~sulfurreducens are closely related, the conductivities of their e-pili differ by more than 3 orders of magnitude. The ability to produce e-pili with high conductivity without generating a genetically modified product enhances the attractiveness of this novel electronic material.

}, keywords = {Electric Conductivity, Electrodes, Electron Transport, Ferric Compounds, Fimbriae Proteins, Gene Expression, Geobacter, Oxidation-Reduction, Recombinant Proteins}, issn = {2150-7511}, doi = {10.1128/mBio.02203-16}, author = {Tan, Yang and Adhikari, Ramesh Y and Malvankar, Nikhil S and Ward, Joy E and Woodard, Trevor L and Nevin, Kelly P and Lovley, Derek R} } @article {3107, title = {Protozoan grazing reduces the current output of microbial fuel cells.}, journal = {Bioresour Technol}, volume = {193}, year = {2015}, month = {2015 Oct}, pages = {8-14}, abstract = {

Several experiments were conducted to determine whether protozoan grazing can reduce current output from sediment microbial fuel cells. When marine sediments were amended with eukaryotic inhibitors, the power output from the fuel cells increased 2-5-fold. Quantitative PCR showed that Geobacteraceae sequences were 120 times more abundant on anodes from treated fuel cells compared to untreated fuel cells, and that Spirotrichea sequences in untreated fuel cells were 200 times more abundant on anode surfaces than in the surrounding sediments. Defined studies with current-producing biofilms of Geobacter sulfurreducens and pure cultures of protozoa demonstrated that protozoa that were effective in consuming G. sulfurreducens reduced current production up to 91\% when added to G. sulfurreducens fuel cells. These results suggest that anode biofilms are an attractive food source for protozoa and that protozoan grazing can be an important factor limiting the current output of sediment microbial fuel cells.

}, keywords = {Bioelectric Energy Sources, Biofilms, Electricity, Electrodes, Eukaryota, Geobacter, Geologic Sediments}, issn = {1873-2976}, doi = {10.1016/j.biortech.2015.06.056}, author = {Holmes, Dawn E and Nevin, Kelly P and Snoeyenbos-West, Oona L and Woodard, Trevor L and Strickland, Justin N and Lovley, Derek R} } @article {3135, title = {Sulfur oxidation to sulfate coupled with electron transfer to electrodes by Desulfuromonas strain TZ1.}, journal = {Microbiology (Reading)}, volume = {160}, year = {2014}, month = {2014 Jan}, pages = {123-129}, abstract = {

Microbial oxidation of elemental sulfur with an electrode serving as the electron acceptor is of interest because this may play an important role in the recovery of electrons from sulfidic wastes and for current production in marine benthic microbial fuel cells. Enrichments initiated with a marine sediment inoculum, with elemental sulfur as the electron donor and a positively poised (+300 mV versus Ag/AgCl) anode as the electron acceptor, yielded an anode biofilm with a diversity of micro-organisms, including Thiobacillus, Sulfurimonas, Pseudomonas, Clostridium and Desulfuromonas species. Further enrichment of the anode biofilm inoculum in medium with elemental sulfur as the electron donor and Fe(III) oxide as the electron acceptor, followed by isolation in solidified sulfur/Fe(III) medium yielded a strain of Desulfuromonas, designated strain TZ1. Strain TZ1 effectively oxidized elemental sulfur to sulfate with an anode serving as the sole electron acceptor, at rates faster than Desulfobulbus propionicus, the only other organism in pure culture previously shown to oxidize S{\textdegree} with current production. The abundance of Desulfuromonas species enriched on the anodes of marine benthic fuel cells has previously been interpreted as acetate oxidation driving current production, but the results presented here suggest that sulfur-driven current production is a likely alternative.

}, keywords = {Bioelectric Energy Sources, Desulfuromonas, DNA, Bacterial, Electricity, Electrodes, Geologic Sediments, Molecular Sequence Data, Oxidation-Reduction, Sequence Analysis, DNA, Sulfates, Sulfur}, issn = {1465-2080}, doi = {10.1099/mic.0.069930-0}, author = {Zhang, Tian and Bain, Timothy S and Barlett, Melissa A and Dar, Shabir A and Snoeyenbos-West, Oona L and Nevin, Kelly P and Lovley, Derek R} } @article {3142, title = {Aromatic amino acids required for pili conductivity and long-range extracellular electron transport in Geobacter sulfurreducens.}, journal = {mBio}, volume = {4}, year = {2013}, month = {2013 Mar 12}, pages = {e00105-13}, abstract = {

UNLABELLED: It has been proposed that Geobacter sulfurreducens requires conductive pili for long-range electron transport to Fe(III) oxides and for high-density current production in microbial fuel cells. In order to investigate this further, we constructed a strain of G. sulfurreducens, designated Aro-5, which produced pili with diminished conductivity. This was accomplished by modifying the amino acid sequence of PilA, the structural pilin protein. An alanine was substituted for each of the five aromatic amino acids in the carboxyl terminus of PilA, the region in which G. sulfurreducens PilA differs most significantly from the PilAs of microorganisms incapable of long-range extracellular electron transport. Strain Aro-5 produced pili that were properly decorated with the multiheme c-type cytochrome OmcS, which is essential for Fe(III) oxide reduction. However, pili preparations of the Aro-5 strain had greatly diminished conductivity and Aro-5 cultures were severely limited in their capacity to reduce Fe(III) compared to the control strain. Current production of the Aro-5 strain, with a graphite anode serving as the electron acceptor, was less than 10\% of that of the control strain. The conductivity of the Aro-5 biofilms was 10-fold lower than the control strain{\textquoteright}s. These results demonstrate that the pili of G. sulfurreducens must be conductive in order for the cells to be effective in extracellular long-range electron transport.

IMPORTANCE: Extracellular electron transfer by Geobacter species plays an important role in the biogeochemistry of soils and sediments and has a number of bioenergy applications. For example, microbial reduction of Fe(III) oxide is one of the most geochemically significant processes in anaerobic soils, aquatic sediments, and aquifers, and Geobacter organisms are often abundant in such environments. Geobacter sulfurreducens produces the highest current densities of any known pure culture, and close relatives are often the most abundant organisms colonizing anodes in microbial fuel cells that harvest electricity from wastewater or aquatic sediments. The finding that a strain of G. sulfurreducens that produces pili with low conductivity is limited in these extracellular electron transport functions provides further insight into these environmentally significant processes.

}, keywords = {Amino Acids, Aromatic, Bioelectric Energy Sources, Biofilms, Electricity, Electrodes, Electron Transport, Ferric Compounds, Fimbriae Proteins, Fimbriae, Bacterial, Geobacter, Graphite}, issn = {2150-7511}, doi = {10.1128/mBio.00105-13}, author = {Vargas, Madeline and Malvankar, Nikhil S and Tremblay, Pier-Luc and Leang, Ching and Smith, Jessica A and Patel, Pranav and Snoeyenbos-West, Oona and Nevin, Kelly P and Lovley, Derek R} } @article {3153, title = {Bioremediation of uranium-contaminated groundwater: a systems approach to subsurface biogeochemistry.}, journal = {Curr Opin Biotechnol}, volume = {24}, year = {2013}, month = {2013 Jun}, pages = {489-97}, abstract = {

Adding organic electron donors to stimulate microbial reduction of highly soluble U(VI) to less soluble U(IV) is a promising strategy for immobilizing uranium in contaminated subsurface environments. Studies suggest that diagnosing the in situ physiological status of the subsurface community during uranium bioremediation with environmental transcriptomic and proteomic techniques can identify factors potentially limiting U(VI) reduction activity. Models which couple genome-scale in silico representations of the metabolism of key microbial populations with geochemical and hydrological models may be able to predict the outcome of bioremediation strategies and aid in the development of new approaches. Concerns remain about the long-term stability of sequestered U(IV) minerals and the release of co-contaminants associated with Fe(III) oxides, which might be overcome through targeted delivery of electrons to select microorganisms using in situ electrodes.

}, keywords = {Biodegradation, Environmental, Electrodes, Ferric Compounds, Genomics, Groundwater, Proteomics, Uranium, Water Pollutants, Radioactive}, issn = {1879-0429}, doi = {10.1016/j.copbio.2012.10.008}, author = {Williams, Kenneth H and Bargar, John R and Lloyd, Jonathan R and Lovley, Derek R} } @article {3139, title = {Improved cathode for high efficient microbial-catalyzed reduction in microbial electrosynthesis cells.}, journal = {Phys Chem Chem Phys}, volume = {15}, year = {2013}, month = {2013 Sep 14}, pages = {14290-4}, abstract = {

Microbial electrosynthesis cells (MECs) are devices wherein microorganisms can electrochemically interact with electrodes, directly donating or accepting electrons from electrode surfaces. Here, we developed a novel cathode by using nickel nanowires anchored to graphite for the improvement of microbial-catalyzed reduction in MEC cathode chamber. This porous nickel-nanowire-network-coated graphite electrode increased the interfacial area and interfacial interactions between the cathode surface and the microbial biofilm. A 2.3 fold increase in bio-reduction rate over the untreated graphite was observed. Around 282 mM day(-1) m(-2) of acetate resulting from the bio-reduction of carbon dioxide by Sporomusa was produced with 82 {\textpm} 14\% of the electrons consumed being recovered in acetate.

}, keywords = {Biocatalysis, Bioelectric Energy Sources, Biofilms, Carbon Dioxide, Electrochemical Techniques, Electrodes, Graphite, Nanowires, Nickel, Oxidation-Reduction, Veillonellaceae}, issn = {1463-9084}, doi = {10.1039/c3cp52697f}, author = {Nie, Huarong and Zhang, Tian and Cui, Mengmeng and Lu, Haiyun and Lovley, Derek R and Russell, Thomas P} } @article {3141, title = {When is a microbial culture "pure"? Persistent cryptic contaminant escapes detection even with deep genome sequencing.}, journal = {mBio}, volume = {4}, year = {2013}, month = {2013 Mar 12}, pages = {e00591-12}, abstract = {

UNLABELLED: Geobacter sulfurreducens strain KN400 was recovered in previous studies in which a culture of the DL1 strain of G. sulfurreducens served as the inoculum in investigations of microbial current production at low anode potentials (-400 mV versus Ag/AgCl). Differences in the genome sequences of KN400 and DL1 were too great to have arisen from adaptive evolution during growth on the anode. Previous deep sequencing (80-fold coverage) of the DL1 culture failed to detect sequences specific to KN400, suggesting that KN400 was an external contaminant inadvertently introduced into the anode culturing system. In order to evaluate this further, a portion of the gene for OmcS, a c-type cytochrome that both KN400 and DL1 possess, was amplified from the DL1 culture. HiSeq-2000 Illumina sequencing of the PCR product detected the KN400 sequence, which differs from the DL1 sequence at 14 bp, at a frequency of ca. 1 in 10(5) copies of the DL1 sequence. A similar low frequency of KN400 was detected with quantitative PCR of a KN400-specific gene. KN400 persisted at this frequency after intensive restreaking of isolated colonies from the DL1 culture. However, a culture in which KN400 could no longer be detected was obtained by serial dilution to extinction in liquid medium. The KN400-free culture could not grow on an anode poised at -400 mV. Thus, KN400 cryptically persisted in the culture dominated by DL1 for more than a decade, undetected by even deep whole-genome sequencing, and was only fortuitously uncovered by the unnatural selection pressure of growth on a low-potential electrode.

IMPORTANCE: Repeated streaking of isolated colonies on solidified medium remains a common strategy for obtaining pure cultures, especially of difficult-to-cultivate microorganisms such as strict anaerobes. The results presented here demonstrate that verifying the purity of cultures obtained in this manner may be difficult because extremely rare variants can persist, undetectable with even deep genomic DNA sequencing. The only way to ensure that a culture is pure is to cultivate it from an initial single cell, which may be technically difficult for many environmentally significant microbes.

}, keywords = {Coinfection, Electrodes, Genes, Bacterial, Genotype, Geobacter, High-Throughput Nucleotide Sequencing, Microbial Interactions, Polymerase Chain Reaction}, issn = {2150-7511}, doi = {10.1128/mBio.00591-12}, author = {Shrestha, Pravin Malla and Nevin, Kelly P and Shrestha, Minita and Lovley, Derek R} } @article {414, title = {Supercapacitors based on c-type cytochromes using conductive nanostructured networks of living bacteria.}, journal = {Chemphyschem}, volume = {13}, year = {2012}, month = {2012 Feb}, pages = {463-8}, abstract = {Supercapacitors have attracted interest in energy storage because they have the potential to complement or replace batteries. Here, we report that c-type cytochromes, naturally immersed in a living, electrically conductive microbial biofilm, greatly enhance the device capacitance by over two orders of magnitude. We employ genetic engineering, protein unfolding and Nernstian modeling for in vivo demonstration of charge storage capacity of c-type cytochromes and perform electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge cycling to confirm the pseudocapacitive, redox nature of biofilm capacitance. The biofilms also show low self-discharge and good charge/discharge reversibility. The superior electrochemical performance of the biofilm is related to its high abundance of cytochromes, providing large electron storage capacity, its nanostructured network with metallic-like conductivity, and its porous architecture with hydrous nature, offering prospects for future low cost and environmentally sustainable energy storage devices.}, keywords = {Bacteria, Biofilms, Cytochrome c Group, Dielectric Spectroscopy, Electric Capacitance, Electrodes, Geobacter, Nanostructures, Oxidation-Reduction}, issn = {1439-7641}, doi = {10.1002/cphc.201100865}, author = {Malvankar, Nikhil S and Mester, T{\"u}nde and Tuominen, Mark T and Lovley, Derek R} } @article {424, title = {Electrosynthesis of organic compounds from carbon dioxide is catalyzed by a diversity of acetogenic microorganisms.}, journal = {Appl Environ Microbiol}, volume = {77}, year = {2011}, month = {2011 May}, pages = {2882-6}, abstract = {Microbial electrosynthesis, a process in which microorganisms use electrons derived from electrodes to reduce carbon dioxide to multicarbon, extracellular organic compounds, is a potential strategy for capturing electrical energy in carbon-carbon bonds of readily stored and easily distributed products, such as transportation fuels. To date, only one organism, the acetogen Sporomusa ovata, has been shown to be capable of electrosynthesis. The purpose of this study was to determine if a wider range of microorganisms is capable of this process. Several other acetogenic bacteria, including two other Sporomusa species, Clostridium ljungdahlii, Clostridium aceticum, and Moorella thermoacetica, consumed current with the production of organic acids. In general acetate was the primary product, but 2-oxobutyrate and formate also were formed, with 2-oxobutyrate being the predominant identified product of electrosynthesis by C. aceticum. S. sphaeroides, C. ljungdahlii, and M. thermoacetica had high (>80\%) efficiencies of electrons consumed and recovered in identified products. The acetogen Acetobacterium woodii was unable to consume current. These results expand the known range of microorganisms capable of electrosynthesis, providing multiple options for the further optimization of this process.}, keywords = {Acetobacterium, Carbon Dioxide, Clostridium, Electrodes, Electrons, Moorella, Organic Chemicals, Oxidation-Reduction, Veillonellaceae}, issn = {1098-5336}, doi = {10.1128/AEM.02642-10}, author = {Nevin, Kelly P and Hensley, Sarah A and Franks, Ashley E and Summers, Zarath M and Ou, Jianhong and Woodard, Trevor L and Snoeyenbos-West, Oona L and Lovley, Derek R} } @article {437, title = {Gene expression and deletion analysis of mechanisms for electron transfer from electrodes to Geobacter sulfurreducens.}, journal = {Bioelectrochemistry}, volume = {80}, year = {2011}, month = {2011 Feb}, pages = {142-50}, abstract = {Geobacter sulfurreducens is one of the few microorganisms available in pure culture known to directly accept electrons from a negatively poised electrode. Microarray analysis was used to compare gene transcript abundance in biofilms of G. sulfurreducens using a graphite electrode as the sole electron donor for fumarate reduction compared with transcript abundance in biofilms growing on the same material, but not consuming current. Surprisingly, genes for putative cell-electrode connections, such as outer-surface cytochromes and pili, which are highly expressed in current-producing biofilms, were not highly expressed in current-consuming biofilms. Microarray analysis of G. sulfurreducens gene transcript abundance in current-consuming biofilms versus current-producing biofilms gave similar results. In both comparative studies current-consuming biofilms had greater transcript abundance for a gene (GSU3274) encoding a putative monoheme, c-type cytochrome. Deletion of genes for outer-surface proteins previously shown to be essential for optimal electron transfer to electrodes had no impact on electron transfer from electrodes. Deletion of GSU3274 completely inhibited electron transfer from electrodes, but had no impact on electron transfer to electrodes. These differences in gene expression patterns and the impact of gene deletions suggest that the mechanisms for electron transfer from electrodes to G. sulfurreducens differ significantly from the mechanisms for electron transfer to electrodes.}, keywords = {Bacterial Proteins, Biofilms, Cytochromes, Electrodes, Electron Transport, Electrons, Gene Expression, Geobacter, Graphite, Oligonucleotide Array Sequence Analysis, Oxidation-Reduction, Sequence Deletion}, issn = {1878-562X}, doi = {10.1016/j.bioelechem.2010.07.005}, author = {Strycharz, Sarah M and Glaven, Richard H and Coppi, Maddalena V and Gannon, Sarah M and Perpetua, Lorrie A and Liu, Anna and Nevin, Kelly P and Lovley, Derek R} } @article {425, title = {A shift in the current: new applications and concepts for microbe-electrode electron exchange.}, journal = {Curr Opin Biotechnol}, volume = {22}, year = {2011}, month = {2011 Jun}, pages = {441-8}, abstract = {Perceived applications of microbe-electrode interactions are shifting from production of electric power to other technologies, some of which even consume current. Electrodes can serve as stable, long-term electron acceptors for contaminant-degrading microbes to promote rapid degradation of organic pollutants in anaerobic subsurface environments. Solar and other forms of renewable electrical energy can be used to provide electrons extracted from water to microorganisms on electrodes at suitably low potentials for a number of groundwater bioremediation applications as well as for the production of fuels and other organic compounds from carbon dioxide. The understanding of how microorganisms exchange electrons with electrodes has improved substantially and is expected to be helpful in optimizing practical applications of microbe-electrode interactions, as well as yielding insights into related natural environmental phenomena.}, keywords = {Bacteria, Biodegradation, Environmental, Biofuels, Carbon Dioxide, Electricity, Electrodes, Electrons, Environmental Pollutants, Fungi, Microbiological Phenomena, Organic Chemicals}, issn = {1879-0429}, doi = {10.1016/j.copbio.2011.01.009}, author = {Lovley, Derek R and Nevin, Kelly P} } @article {453, title = {Electrode-based approach for monitoring in situ microbial activity during subsurface bioremediation.}, journal = {Environ Sci Technol}, volume = {44}, year = {2010}, month = {2010 Jan 1}, pages = {47-54}, abstract = {Current production by microorganisms colonizing subsurface electrodes and its relationship to substrate availability and microbial activity was evaluated in an aquifer undergoing bioremediation. Borehole graphite anodes were installed downgradient from a region of acetate injection designed to stimulate bioreduction of U(VI); cathodes consisted of graphite electrodes embedded at the ground surface. Significant increases in current density (< or =50 mA/m2) tracked delivery of acetate to the electrodes, dropping rapidly when acetate inputs were discontinued. An upgradient control electrode not exposed to acetate produced low, steady currents (< or =0.2 mA/m2). Elevated current was strongly correlated with uranium removal but minimal correlation existed with elevated Fe(II). Confocal laser scanning microscopy of electrodes revealed firmly attached biofilms, and analysis of 16S rRNA gene sequences indicated the electrode surfaces were dominated (67-80\%) by Geobacter species. This is the first demonstration that electrodes can produce readily detectable currents despite long-range (6 m) separation of anode and cathode, and these results suggest that oxidation of acetate coupled to electron transfer to electrodes by Geobacter species was the primary source of current. Thus it is expected that current production may serve as an effective proxy for monitoring in situ microbial activity in a variety of subsurface anoxic environments.}, keywords = {Electrodes, Environmental Monitoring, Environmental Remediation, Geobacter, RNA, Ribosomal, 16S, Water Pollutants, Chemical}, issn = {0013-936X}, doi = {10.1021/es9017464}, author = {Williams, Kenneth H and Nevin, Kelly P and Franks, Ashley and Englert, Andreas and Long, Philip E and Lovley, Derek R} } @article {450, title = {Microtoming coupled to microarray analysis to evaluate the spatial metabolic status of Geobacter sulfurreducens biofilms.}, journal = {ISME J}, volume = {4}, year = {2010}, month = {2010 Apr}, pages = {509-19}, abstract = {Further insight into the metabolic status of cells within anode biofilms is essential for understanding the functioning of microbial fuel cells and developing strategies to optimize their power output. Cells throughout anode biofilms of Geobacter sulfurreducens reduced the metabolic stains: 5-cyano-2,3-ditolyl tetrazolium chloride and Redox Green, suggesting metabolic activity throughout the biofilm. To compare the metabolic status of cells growing close to the anode versus cells in the outer portion of the anode biofilm, anode biofilms were encased in resin and sectioned into inner (0-20 microm from anode surface) and outer (30-60 microm) fractions. Transcriptional analysis revealed that, at a twofold threshold, 146 genes had significant (P<0.05) differences in transcript abundance between the inner and outer biofilm sections. Only 1 gene, GSU0093, a hypothetical ATP-binding cassette transporter, had significantly higher transcript abundances in the outer biofilm. Genes with lower transcript abundance in the outer biofilm included genes for ribosomal proteins and NADH dehydrogenase, suggesting lower metabolic rates. However, differences in transcript abundance were relatively low (50 microm) biofilms to electrodes acting as a sole electron acceptor were investigated. Biofilms of Geobacter sulfurreducens were grown either in flow-through systems with graphite anodes as the electron acceptor or on the same graphite surface, but with fumarate as the sole electron acceptor. Fumarate-grown biofilms were not immediately capable of significant current production, suggesting substantial physiological differences from current-producing biofilms. Microarray analysis revealed 13 genes in current-harvesting biofilms that had significantly higher transcript levels. The greatest increases were for pilA, the gene immediately downstream of pilA, and the genes for two outer c-type membrane cytochromes, OmcB and OmcZ. Down-regulated genes included the genes for the outer-membrane c-type cytochromes, OmcS and OmcT. Results of quantitative RT-PCR of gene transcript levels during biofilm growth were consistent with microarray results. OmcZ and the outer-surface c-type cytochrome, OmcE, were more abundant and OmcS was less abundant in current-harvesting cells. Strains in which pilA, the gene immediately downstream from pilA, omcB, omcS, omcE, or omcZ was deleted demonstrated that only deletion of pilA or omcZ severely inhibited current production and biofilm formation in current-harvesting mode. In contrast, these gene deletions had no impact on biofilm formation on graphite surfaces when fumarate served as the electron acceptor. These results suggest that biofilms grown harvesting current are specifically poised for electron transfer to electrodes and that, in addition to pili, OmcZ is a key component in electron transfer through differentiated G. sulfurreducens biofilms to electrodes.}, keywords = {Amino Acid Sequence, Bacterial Outer Membrane Proteins, Bioelectric Energy Sources, Biofilms, Cytochromes, Electrodes, Electron Transport, Fumarates, Gene Deletion, Gene Expression Profiling, Gene Expression Regulation, Bacterial, Genetic Complementation Test, Geobacter, Microscopy, Confocal, Molecular Sequence Data, Oligonucleotide Array Sequence Analysis, Oxidation-Reduction, RNA, Messenger, Up-Regulation}, issn = {1932-6203}, doi = {10.1371/journal.pone.0005628}, author = {Nevin, Kelly P and Kim, Byoung-Chan and Glaven, Richard H and Johnson, Jessica P and Woodard, Trevor L and Meth{\'e}, Barbara A and Didonato, Raymond J and Covalla, Sean F and Franks, Ashley E and Liu, Anna and Lovley, Derek R} } @article {487, title = {Electricity generation by Geobacter sulfurreducens attached to gold electrodes.}, journal = {Langmuir}, volume = {24}, year = {2008}, month = {2008 Apr 15}, pages = {4376-9}, abstract = {The versatility of gold for electrode manufacture suggests that it could be an ideal material for some microbial fuel cell applications. However, previous studies have suggested that microorganisms that readily transfer electrons to graphite do not transfer electrons to gold. Investigations with Geobacter sulfurreducens demonstrated that it could grow on gold anodes producing current nearly as effectively as with graphite anodes. Current production was associated with the development of G. sulfurreducens biofilms up to 40 microm thick. No current was produced if pilA, the gene for the structural protein of the conductive pili of G. sulfurreducens, was deleted. The finding that gold is a suitable anode material for microbial fuel cells offers expanded possibilities for the construction of microbial fuel cells and the electrochemical analysis of microbe-electrode interactions.}, keywords = {Electrodes, Electrons, Geobacter, Gold, Microscopy, Confocal, Microscopy, Electron, Scanning, Surface Properties}, issn = {0743-7463}, doi = {10.1021/la703469y}, author = {Richter, Hanno and McCarthy, Kevin and Nevin, Kelly P and Johnson, Jessica P and Rotello, Vincent M and Lovley, Derek R} } @article {483, title = {Genes for two multicopper proteins required for Fe(III) oxide reduction in Geobacter sulfurreducens have different expression patterns both in the subsurface and on energy-harvesting electrodes.}, journal = {Microbiology}, volume = {154}, year = {2008}, month = {2008 May}, pages = {1422-35}, abstract = {Previous studies have shown that Geobacter sulfurreducens requires the outer-membrane, multicopper protein OmpB for Fe(III) oxide reduction. A homologue of OmpB, designated OmpC, which is 36 \% similar to OmpB, has been discovered in the G. sulfurreducens genome. Deletion of ompC inhibited reduction of insoluble, but not soluble Fe(III). Analysis of multiple Geobacter and Pelobacter genomes, as well as in situ Geobacter, indicated that genes encoding multicopper proteins are conserved in Geobacter species but are not found in Pelobacter species. Levels of ompB transcripts were similar in G. sulfurreducens at different growth rates in chemostats and during growth on a microbial fuel cell anode. In contrast, ompC transcript levels increased at higher growth rates in chemostats and with increasing current production in fuel cells. Constant levels of Geobacter ompB transcripts were detected in groundwater during a field experiment in which acetate was added to the subsurface to promote in situ uranium bioremediation. In contrast, ompC transcript levels increased during the rapid phase of growth of Geobacter species following addition of acetate to the groundwater and then rapidly declined. These results demonstrate that more than one multicopper protein is required for optimal Fe(III) oxide reduction in G. sulfurreducens and suggest that, in environmental studies, quantifying OmpB/OmpC-related genes could help alleviate the problem that Pelobacter genes may be inadvertently quantified via quantitative analysis of 16S rRNA genes. Furthermore, comparison of differential expression of ompB and ompC may provide insight into the in situ metabolic state of Geobacter species in environments of interest.}, keywords = {Acetates, Amino Acid Sequence, Bacterial Outer Membrane Proteins, Electrodes, Ferric Compounds, Gene Deletion, Gene Expression Profiling, Geobacter, Molecular Sequence Data, Oxidation-Reduction, Phylogeny, Sequence Alignment, Sequence Homology, Nucleic Acid, Soil Microbiology, Uranium}, issn = {1350-0872}, doi = {10.1099/mic.0.2007/014365-0}, author = {Holmes, Dawn E and Mester, T{\"u}nde and O{\textquoteright}Neil, Regina A and Perpetua, Lorrie A and Larrahondo, M Juliana and Glaven, Richard and Sharma, Manju L and Ward, Joy E and Nevin, Kelly P and Lovley, Derek R} } @article {475, title = {Graphite electrode as a sole electron donor for reductive dechlorination of tetrachlorethene by Geobacter lovleyi.}, journal = {Appl Environ Microbiol}, volume = {74}, year = {2008}, month = {2008 Oct}, pages = {5943-7}, abstract = {The possibility that graphite electrodes can serve as the direct electron donor for microbially catalyzed reductive dechlorination was investigated with Geobacter lovleyi. In an initial evaluation of whether G. lovleyi could interact electronically with graphite electrodes, cells were provided with acetate as the electron donor and an electrode as the sole electron acceptor. Current was produced at levels that were ca. 10-fold lower than those previously reported for Geobacter sulfurreducens under similar conditions, and G. lovleyi anode biofilms were correspondingly thinner. When an electrode poised at -300 mV (versus a standard hydrogen electrode) was provided as the electron donor, G. lovleyi effectively reduced fumarate to succinate. The stoichiometry of electrons consumed to succinate produced was 2:1, the ratio expected if the electrode served as the sole electron donor for fumarate reduction. G. lovleyi effectively reduced tetrachloroethene (PCE) to cis-dichloroethene with a poised electrode as the sole electron donor at rates comparable to those obtained when acetate serves as the electron donor. Cells were less abundant on the electrodes when the electrodes served as an electron donor than when they served as an electron acceptor. PCE was not reduced in controls without cells or when the current supply to cells was interrupted. These results demonstrate that G. lovleyi can use a poised electrode as a direct electron donor for reductive dechlorination of PCE. The ability to colocalize dechlorinating microorganisms with electrodes has several potential advantages for bioremediation of subsurface chlorinated contaminants, especially in source zones where electron donor delivery is challenging and often limits dechlorination.}, keywords = {Acetic Acid, Biofilms, Biomass, Electricity, Electrodes, Electrons, Ethylene Dichlorides, Fumarates, Geobacter, Graphite, Microscopy, Electron, Scanning, Succinic Acid, Tetrachloroethylene}, issn = {1098-5336}, doi = {10.1128/AEM.00961-08}, author = {Strycharz, Sarah M and Woodard, Trevor L and Johnson, Jessica P and Nevin, Kelly P and Sanford, Robert A and L{\"o}ffler, Frank E and Lovley, Derek R} } @article {468, title = {The microbe electric: conversion of organic matter to electricity.}, journal = {Curr Opin Biotechnol}, volume = {19}, year = {2008}, month = {2008 Dec}, pages = {564-71}, abstract = {Broad application of microbial fuel cells will require substantial increases in current density. A better understanding of the microbiology of these systems may help. Recent studies have greatly expanded the range of microorganisms known to function either as electrode-reducing microorganisms at the anode or as electrode-oxidizing microorganisms at the cathode. Microorganisms that can completely oxidize organic compounds with an electrode serving as the sole electron acceptor are expected to be the primary contributors to power production. Several mechanisms for electron transfer to anodes have been proposed including: direct electron transfer via outer-surface c-type cytochromes, long-range electron transfer via microbial nanowires, electron flow through a conductive biofilm matrix containing cytochromes, and soluble electron shuttles. Which mechanisms are most important depend on the microorganisms and the thickness of the anode biofilm. Emerging systems biology approaches to the study, design, and evolution of microorganisms interacting with electrodes are expected to contribute to improved microbial fuel cells.}, keywords = {Bacteria, Bioelectric Energy Sources, Electricity, Electrodes, Organic Chemicals, Oxidation-Reduction}, issn = {1879-0429}, doi = {10.1016/j.copbio.2008.10.005}, author = {Lovley, Derek R} } @article {479, title = {Power output and columbic efficiencies from biofilms of Geobacter sulfurreducens comparable to mixed community microbial fuel cells.}, journal = {Environ Microbiol}, volume = {10}, year = {2008}, month = {2008 Oct}, pages = {2505-14}, abstract = {It has been previously noted that mixed communities typically produce more power in microbial fuel cells than pure cultures. If true, this has important implications for the design of microbial fuel cells and for studying the process of electron transfer on anode biofilms. To further evaluate this, Geobacter sulfurreducens was grown with acetate as fuel in a continuous flow {\textquoteright}ministack{\textquoteright} system in which the carbon cloth anode and cathode were positioned in close proximity, and the cation-selective membrane surface area was maximized in order to overcome some of the electrochemical limitations that were inherent in fuel cells previously employed for the study of pure cultures. Reducing the size of the anode in order to eliminate cathode limitation resulted in maximum current and power densities per m(2) of anode surface of 4.56 A m(-2) and 1.88 W m(-2) respectively. Electron recovery as current from acetate oxidation was c. 100\% when oxygen diffusion into the system was minimized. This performance is comparable to the highest levels previously reported for mixed communities in similar microbial fuel cells and slightly higher than the power output of an anaerobic sludge inoculum in the same ministack system. Minimizing the volume of the anode chamber yielded a volumetric power density of 2.15 kW m(-3), which is the highest power density per volume yet reported for a microbial fuel cell. Geobacter sulfurreducens formed relatively uniform biofilms 3-18 mum thick on the carbon cloth anodes. When graphite sticks served as the anode, the current density (3.10 A m(-2)) was somewhat less than with the carbon cloth anodes, but the biofilms were thicker (c. 50 mum) with a more complex pillar and channel structure. These results suggest that the previously observed disparity in power production in pure and mixed culture microbial fuel cell systems can be attributed more to differences in the fuel cell designs than to any inherent superior capability of mixed cultures to produce more power than pure cultures.}, keywords = {Acetic Acid, Biofilms, Carbon, Electricity, Electrodes, Geobacter, Oxidation-Reduction}, issn = {1462-2920}, doi = {10.1111/j.1462-2920.2008.01675.x}, author = {Nevin, K P and Richter, H and Covalla, S F and Johnson, J P and Woodard, T L and Orloff, A L and Jia, H and Zhang, M and Lovley, D R} } @article {514, title = {Biofilm and nanowire production leads to increased current in Geobacter sulfurreducens fuel cells.}, journal = {Appl Environ Microbiol}, volume = {72}, year = {2006}, month = {2006 Nov}, pages = {7345-8}, abstract = {Geobacter sulfurreducens developed highly structured, multilayer biofilms on the anode surface of a microbial fuel cell converting acetate to electricity. Cells at a distance from the anode remained viable, and there was no decrease in the efficiency of current production as the thickness of the biofilm increased. Genetic studies demonstrated that efficient electron transfer through the biofilm required the presence of electrically conductive pili. These pili may represent an electronic network permeating the biofilm that can promote long-range electrical transfer in an energy-efficient manner, increasing electricity production more than 10-fold.}, keywords = {Acetates, Bioelectric Energy Sources, Biofilms, Electricity, Electrodes, Electron Transport, Fimbriae, Bacterial, Geobacter, Microscopy, Confocal, Mutation, Nanowires}, issn = {0099-2240}, doi = {10.1128/AEM.01444-06}, author = {Reguera, Gemma and Nevin, Kelly P and Nicoll, Julie S and Covalla, Sean F and Woodard, Trevor L and Lovley, Derek R} } @article {519, title = {Bug juice: harvesting electricity with microorganisms.}, journal = {Nat Rev Microbiol}, volume = {4}, year = {2006}, month = {2006 Jul}, pages = {497-508}, abstract = {It is well established that some reduced fermentation products or microbially reduced artificial mediators can abiotically react with electrodes to yield a small electrical current. This type of metabolism does not typically result in an efficient conversion of organic compounds to electricity because only some metabolic end products will react with electrodes, and the microorganisms only incompletely oxidize their organic fuels. A new form of microbial respiration has recently been discovered in which microorganisms conserve energy to support growth by oxidizing organic compounds to carbon dioxide with direct quantitative electron transfer to electrodes. These organisms, termed electricigens, offer the possibility of efficiently converting organic compounds into electricity in self-sustaining systems with long-term stability.}, keywords = {Bacteria, Bioelectric Energy Sources, Electricity, Electrodes, Electron Transport, Oxidation-Reduction}, issn = {1740-1526}, doi = {10.1038/nrmicro1442}, author = {Lovley, Derek 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 {513, title = {Microarray and genetic analysis of electron transfer to electrodes in Geobacter sulfurreducens.}, journal = {Environ Microbiol}, volume = {8}, year = {2006}, month = {2006 Oct}, pages = {1805-15}, abstract = {Whole-genome analysis of gene expression in Geobacter sulfurreducens revealed 474 genes with transcript levels that were significantly different during growth with an electrode as the sole electron acceptor versus growth on Fe(III) citrate. The greatest response was a more than 19-fold increase in transcript levels for omcS, which encodes an outer-membrane cytochrome previously shown to be required for Fe(III) oxide reduction. Quantitative reverse transcription polymerase chain reaction and Northern analyses confirmed the higher levels of omcS transcripts, which increased as power production increased. Deletion of omcS inhibited current production that was restored when omcS was expressed in trans. Transcript expression and genetic analysis suggested that OmcE, another outer-membrane cytochrome, is also involved in electron transfer to electrodes. Surprisingly, genes for other proteins known to be important in Fe(III) reduction such as the outer-membrane c-type cytochrome, OmcB, and the electrically conductive pilin "nanowires" did not have higher transcript levels on electrodes, and deletion of the relevant genes did not inhibit power production. Changes in the transcriptome suggested that cells growing on electrodes were subjected to less oxidative stress than cells growing on Fe(III) citrate and that a number of genes annotated as encoding metal efflux proteins or proteins of unknown function may be important for growth on electrodes. These results demonstrate for the first time that it is possible to evaluate gene expression, and hence the metabolic state, of microorganisms growing on electrodes on a genome-wide basis and suggest that OmcS, and to a lesser extent OmcE, are important in electron transfer to electrodes. This has important implications for the design of electrode materials and the genetic engineering of microorganisms to improve the function of microbial fuel cells.}, keywords = {Bacterial Outer Membrane Proteins, Blotting, Northern, Cytochromes c, Electrodes, Electrophysiology, Gene Expression Regulation, Bacterial, Geobacter, Oligonucleotide Array Sequence Analysis, Oxidation-Reduction, Reverse Transcriptase Polymerase Chain Reaction, RNA, Bacterial, RNA, Messenger}, issn = {1462-2912}, doi = {10.1111/j.1462-2920.2006.01065.x}, author = {Holmes, Dawn E and Chaudhuri, Swades K and Nevin, Kelly P and Mehta, Teena and Meth{\'e}, Barbara A and Liu, Anna and Ward, Joy E and Woodard, Trevor L and Webster, Jennifer and Lovley, Derek R} } @article {540, title = {Evidence for involvement of an electron shuttle in electricity generation by Geothrix fermentans.}, journal = {Appl Environ Microbiol}, volume = {71}, year = {2005}, month = {2005 Apr}, pages = {2186-9}, abstract = {In experiments performed using graphite electrodes poised by a potentiostat (+200 mV versus Ag/AgCl) or in a microbial fuel cell (with oxygen as the electron acceptor), the Fe(III)-reducing organism Geothrix fermentans conserved energy to support growth by coupling the complete oxidation of acetate to reduction of a graphite electrode. Other organic compounds, such as lactate, malate, propionate, and succinate as well as components of peptone and yeast extract, were utilized for electricity production. However, electrical characteristics and the results of shuttling assays indicated that unlike previously described electrode-reducing microorganisms, G. fermentans produced a compound that promoted electrode reduction. This is the first report of complete oxidation of organic compounds linked to electrode reduction by an isolate outside of the Proteobacteria.}, keywords = {Acetates, Bacteria, Bioelectric Energy Sources, Electricity, Electrodes, Electron Transport, Graphite, Microscopy, Electron, Scanning, Oxidation-Reduction}, issn = {0099-2240}, doi = {10.1128/AEM.71.4.2186-2189.2005}, author = {Bond, Daniel R and Lovley, Derek R} } @article {529, title = {Potential for quantifying expression of the Geobacteraceae citrate synthase gene to assess the activity of Geobacteraceae in the subsurface and on current-harvesting electrodes.}, journal = {Appl Environ Microbiol}, volume = {71}, year = {2005}, month = {2005 Nov}, pages = {6870-7}, abstract = {The Geobacteraceae citrate synthase is phylogenetically distinct from those of other prokaryotes and is a key enzyme in the central metabolism of Geobacteraceae. Therefore, the potential for using levels of citrate synthase mRNA to estimate rates of Geobacter metabolism was evaluated in pure culture studies and in four different Geobacteraceae-dominated environments. Quantitative reverse transcription-PCR studies with mRNA extracted from cultures of Geobacter sulfurreducens grown in chemostats with Fe(III) as the electron acceptor or in batch with electrodes as the electron acceptor indicated that transcript levels of the citrate synthase gene, gltA, increased with increased rates of growth/Fe(III) reduction or current production, whereas the expression of the constitutively expressed housekeeping genes recA, rpoD, and proC remained relatively constant. Analysis of mRNA extracted from groundwater collected from a U(VI)-contaminated site undergoing in situ uranium bioremediation revealed a remarkable correspondence between acetate levels in the groundwater and levels of transcripts of gltA. The expression of gltA was also significantly greater in RNA extracted from groundwater beneath a highway runoff recharge pool that was exposed to calcium magnesium acetate in June, when acetate concentrations were high, than in October, when the levels had significantly decreased. It was also possible to detect gltA transcripts on current-harvesting anodes deployed in freshwater sediments. These results suggest that it is possible to monitor the in situ metabolic rate of Geobacteraceae by tracking the expression of the citrate synthase gene.}, keywords = {Acetates, Citrate (si)-Synthase, Deltaproteobacteria, DNA, Ribosomal, Electrodes, Ferric Compounds, Fresh Water, Geobacter, Geologic Sediments, Petroleum, Phylogeny, RNA, Ribosomal, 16S, Uranium, Water Pollutants, Chemical, Water Pollutants, Radioactive}, issn = {0099-2240}, doi = {10.1128/AEM.71.11.6870-6877.2005}, author = {Holmes, Dawn E and Nevin, Kelly P and O{\textquoteright}Neil, Regina A and Ward, Joy E and Adams, Lorrie A and Woodard, Trevor L and Vrionis, Helen A and Lovley, Derek R} } @article {528, title = {Remediation and recovery of uranium from contaminated subsurface environments with electrodes.}, journal = {Environ Sci Technol}, volume = {39}, year = {2005}, month = {2005 Nov 15}, pages = {8943-7}, abstract = {Previous studies have demonstrated that Geobacter species can effectively remove uranium from contaminated groundwater by reducing soluble U(VI) to the relatively insoluble U(IV) with organic compounds serving as the electron donor. Studies were conducted to determine whether electrodes might serve as an alternative electron donor for U(VI) reduction by a pure culture of Geobacter sulfurreducens and microorganisms in uranium-contaminated sediments. Electrodes poised at -500 mV (vs a Ag/AgCl reference) rapidly removed U(VI) from solution in the absence of cells. However, when the poise at the electrode was removed, all of the U(VI) returned to solution, demonstrating that the electrode did not reduce U(VI). If G. sulfurreducens was present on the electrode, U(VI) did not return to solution until the electrode was exposed to dissolved oxygen. This suggeststhat G. sulfurreducens on the electrode reduced U(VI) to U(IV) which was stably precipitated until reoxidized in the presence of oxygen. When an electrode was placed in uranium-contaminated subsurface sediments, U(VI) was removed and recovered from groundwater using poised electrodes. Electrodes emplaced in flow-through columns of uranium-contaminated sediments readily removed U(VI) from the groundwater, and 87\% of the uranium that had been removed was recovered from the electrode surface after the electrode was pulled from the sediments. These results suggest that microorganisms can use electrons derived from electrodes to reduce U(VI) and that it may be possible to remove and recover uranium from contaminated groundwater with poised electrodes.}, keywords = {Biodegradation, Environmental, Electrodes, Geobacter, Graphite, Soil Pollutants, Uranium, Water Pollutants, Chemical}, issn = {0013-936X}, author = {Gregory, Kelvin B and Lovley, Derek R} } @article {559, title = {Electron transfer by Desulfobulbus propionicus to Fe(III) and graphite electrodes.}, journal = {Appl Environ Microbiol}, volume = {70}, year = {2004}, month = {2004 Feb}, pages = {1234-7}, abstract = {Desulfobulbus propionicus was able to grow with Fe(III), the humic acids analog anthraquinone-2,6-disulfonate (AQDS), or a graphite electrode as an electron acceptor. These results provide an explanation for the enrichment of Desulfobulbaceae species on the surface of electrodes harvesting electricity from anaerobic marine sediments and further expand the diversity of microorganisms known to have the ability to use both sulfate and Fe(III) as an electron acceptor.}, keywords = {Culture Media, Deltaproteobacteria, Electrodes, Electron Transport, Ferric Compounds, Graphite, Oxidation-Reduction, Pyruvic Acid, Sulfates}, issn = {0099-2240}, author = {Holmes, Dawn E and Bond, Daniel R 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} } @article {544, title = {Microbial communities associated with electrodes harvesting electricity from a variety of aquatic sediments.}, journal = {Microb Ecol}, volume = {48}, year = {2004}, month = {2004 Aug}, pages = {178-90}, abstract = {The microbial communities associated with electrodes from underwater fuel cells harvesting electricity from five different aquatic sediments were investigated. Three fuel cells were constructed with marine, salt-marsh, or freshwater sediments incubated in the laboratory. Fuel cells were also deployed in the field in salt marsh sediments in New Jersey and estuarine sediments in Oregon, USA. All of the sediments produced comparable amounts of power. Analysis of 16S rRNA gene sequences after 3-7 months of incubation demonstrated that all of the energy-harvesting anodes were highly enriched in microorganisms in the delta-Proteobacteria when compared with control electrodes not connected to a cathode. Geobacteraceae accounted for the majority of delta-Proteobacterial sequences or all of the energy-harvesting anodes, except the one deployed at the Oregon estuarine site. Quantitative PCR analysis of 16S rRNA genes and culturing studies indicated that Geobacteraceae were 100-fold more abundant on the marine-deployed anodes versus controls. Sequences most similar to microorganisms in the family Desulfobulbaceae predominated on the anode deployed in the estuarine sediments, and a significant proportion of the sequences recovered from the freshwater anodes were closely related to the Fe(III)-reducing isolate, Geothrix fermentans. There was also a specific enrichment of microorganisms on energy harvesting cathodes, but the enriched populations varied with the sediment/water source. Thus, future studies designed to help optimize the harvesting of electricity from aquatic sediments or waste organic matter should focus on the electrode interactions of these microorganisms which are most competitive in colonizing anodes and cathodes.}, keywords = {Base Sequence, Biodiversity, Bioelectric Energy Sources, Cloning, Molecular, DNA Primers, Electrodes, Gammaproteobacteria, Geologic Sediments, Molecular Sequence Data, Phylogeny, Polymerase Chain Reaction, Restriction Mapping, RNA, Ribosomal, 16S, Sequence Analysis, DNA}, issn = {0095-3628}, doi = {10.1007/s00248-003-0004-4}, author = {Holmes, D E and Bond, D R and O{\textquoteright}Neil, R A and Reimers, C E and Tender, L R and Lovley, D R} } @article {564, title = {Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells.}, journal = {Nat Biotechnol}, volume = {21}, year = {2003}, month = {2003 Oct}, pages = {1229-32}, abstract = {Abundant energy, stored primarily in the form of carbohydrates, can be found in waste biomass from agricultural, municipal and industrial sources as well as in dedicated energy crops, such as corn and other grains. Potential strategies for deriving useful forms of energy from carbohydrates include production of ethanol and conversion to hydrogen, but these approaches face technical and economic hurdles. An alternative strategy is direct conversion of sugars to electrical power. Existing transition metal-catalyzed fuel cells cannot be used to generate electric power from carbohydrates. Alternatively, biofuel cells in which whole cells or isolated redox enzymes catalyze the oxidation of the sugar have been developed, but their applicability has been limited by several factors, including (i) the need to add electron-shuttling compounds that mediate electron transfer from the cell to the anode, (ii) incomplete oxidation of the sugars and (iii) lack of long-term stability of the fuel cells. Here we report on a novel microorganism, Rhodoferax ferrireducens, that can oxidize glucose to CO(2) and quantitatively transfer electrons to graphite electrodes without the need for an electron-shuttling mediator. Growth is supported by energy derived from the electron transfer process itself and results in stable, long-term power production.}, keywords = {Bioelectric Energy Sources, Bioreactors, Carbon Dioxide, Comamonadaceae, Electrodes, Energy Transfer, Equipment Design, Equipment Failure Analysis, Glucose, Iron, Oxidation-Reduction}, issn = {1087-0156}, doi = {10.1038/nbt867}, author = {Chaudhuri, Swades K and Lovley, Derek R} } @article {573, title = {Electricity production by Geobacter sulfurreducens attached to electrodes.}, journal = {Appl Environ Microbiol}, volume = {69}, year = {2003}, month = {2003 Mar}, pages = {1548-55}, abstract = {Previous studies have suggested that members of the Geobacteraceae can use electrodes as electron acceptors for anaerobic respiration. In order to better understand this electron transfer process for energy production, Geobacter sulfurreducens was inoculated into chambers in which a graphite electrode served as the sole electron acceptor and acetate or hydrogen was the electron donor. The electron-accepting electrodes were maintained at oxidizing potentials by connecting them to similar electrodes in oxygenated medium (fuel cells) or to potentiostats that poised electrodes at +0.2 V versus an Ag/AgCl reference electrode (poised potential). When a small inoculum of G. sulfurreducens was introduced into electrode-containing chambers, electrical current production was dependent upon oxidation of acetate to carbon dioxide and increased exponentially, indicating for the first time that electrode reduction supported the growth of this organism. When the medium was replaced with an anaerobic buffer lacking nutrients required for growth, acetate-dependent electrical current production was unaffected and cells attached to these electrodes continued to generate electrical current for weeks. This represents the first report of microbial electricity production solely by cells attached to an electrode. Electrode-attached cells completely oxidized acetate to levels below detection (<10 micro M), and hydrogen was metabolized to a threshold of 3 Pa. The rates of electron transfer to electrodes (0.21 to 1.2 micro mol of electrons/mg of protein/min) were similar to those observed for respiration with Fe(III) citrate as the electron acceptor (E(o){\textquoteright} =+0.37 V). The production of current in microbial fuel cell (65 mA/m(2) of electrode surface) or poised-potential (163 to 1,143 mA/m(2)) mode was greater than what has been reported for other microbial systems, even those that employed higher cell densities and electron-shuttling compounds. Since acetate was completely oxidized, the efficiency of conversion of organic electron donor to electricity was significantly higher than in previously described microbial fuel cells. These results suggest that the effectiveness of microbial fuel cells can be increased with organisms such as G. sulfurreducens that can attach to electrodes and remain viable for long periods of time while completely oxidizing organic substrates with quantitative transfer of electrons to an electrode.}, keywords = {Culture Media, Deltaproteobacteria, Electricity, Electrodes, Electron Transport, Microscopy, Electron, Scanning, Oxidation-Reduction}, issn = {0099-2240}, author = {Bond, Daniel R and Lovley, Derek R} } @article {572, title = {Analysis of the genetic potential and gene expression of microbial communities involved in the in situ bioremediation of uranium and harvesting electrical energy from organic matter.}, journal = {OMICS}, volume = {6}, year = {2002}, month = {2002}, pages = {331-9}, abstract = {The proposed research will investigate two microbial communities that are of direct relevance to Department of Energy interests. One is the microbial community associated with the in situ bioremediation of uranium-contaminated groundwater. The second is a microbial community that harvests energy from waste organic matter in the form of electricity. These studies will address DOE needs for (1) remediation of metals and radionuclides at DOE sites and (2) the development of cleaner forms of energy and biomass conversion to energy. Our previous studies have demonstrated that the microbial communities involved in uranium bioremediation and energy harvesting are both dominated by microorganisms in the family Geobacteraceae and that the organisms in this family are responsible for uranium bioremediation and electron transfer to electrodes. The initial objectives of this study are to (1) describe the genetic potential of the Geobacteraceae that predominate in the environments of interest; (2) identify conserved patterns of gene expression within the Geobacteraceae family in response to a range of environmental conditions; (3) begin to identify mechanisms controlling the expression of key genes related to survival, growth, and activity in subsurface environments and on electrodes; and (4) use the results from subobjectives 1-3 to develop a conceptual model for predicting gene expression of Geobacteraceae in the environments of interest. This will serve as the basis for a subsequent simulation model of the growth and activity of Geobacteraceae in the subsurface and on electrodes.}, keywords = {Biodegradation, Environmental, Deltaproteobacteria, Electricity, Electrodes, Energy Metabolism, Gene Expression Regulation, Bacterial, Genome, Bacterial, Geologic Sediments, Models, Theoretical, Uranium}, issn = {1536-2310}, doi = {10.1089/153623102321112755}, author = {Lovley, Derek R} } @article {588, title = {Electrode-reducing microorganisms that harvest energy from marine sediments.}, journal = {Science}, volume = {295}, year = {2002}, month = {2002 Jan 18}, pages = {483-5}, abstract = {Energy in the form of electricity can be harvested from marine sediments by placing a graphite electrode (the anode) in the anoxic zone and connecting it to a graphite cathode in the overlying aerobic water. We report a specific enrichment of microorganisms of the family Geobacteraceae on energy-harvesting anodes, and we show that these microorganisms can conserve energy to support their growth by oxidizing organic compounds with an electrode serving as the sole electron acceptor. This finding not only provides a method for extracting energy from organic matter, but also suggests a strategy for promoting the bioremediation of organic contaminants in subsurface environments.}, keywords = {Aerobiosis, Anaerobiosis, Anthraquinones, Benzoates, Biodegradation, Environmental, Carbon Dioxide, Colony Count, Microbial, Deltaproteobacteria, DNA, Ribosomal, Electricity, Electrodes, Electrons, Energy Metabolism, Geologic Sediments, Oxidation-Reduction, RNA, Ribosomal, 16S, Seawater, Sodium Acetate}, issn = {1095-9203}, doi = {10.1126/science.1066771}, author = {Bond, Daniel R and Holmes, Dawn E and Tender, Leonard M and Lovley, Derek R} } @article {580, title = {Harnessing microbially generated power on the seafloor.}, journal = {Nat Biotechnol}, volume = {20}, year = {2002}, month = {2002 Aug}, pages = {821-5}, abstract = {In many marine environments, a voltage gradient exists across the water sediment interface resulting from sedimentary microbial activity. Here we show that a fuel cell consisting of an anode embedded in marine sediment and a cathode in overlying seawater can use this voltage gradient to generate electrical power in situ. Fuel cells of this design generated sustained power in a boat basin carved into a salt marsh near Tuckerton, New Jersey, and in the Yaquina Bay Estuary near Newport, Oregon. Retrieval and analysis of the Tuckerton fuel cell indicates that power generation results from at least two anode reactions: oxidation of sediment sulfide (a by-product of microbial oxidation of sedimentary organic carbon) and oxidation of sedimentary organic carbon catalyzed by microorganisms colonizing the anode. These results demonstrate in real marine environments a new form of power generation that uses an immense, renewable energy reservoir (sedimentary organic carbon) and has near-immediate application.}, keywords = {Bacteria, Bioelectric Energy Sources, Biotechnology, Carbon, Conservation of Energy Resources, DNA, Ribosomal, Electricity, Electrodes, Environmental Microbiology, Geologic Sediments, Molecular Sequence Data, New Jersey, Oceans and Seas, Oregon, Oxidation-Reduction, RNA, Bacterial, RNA, Ribosomal, 16S, Sulfides}, issn = {1087-0156}, doi = {10.1038/nbt716}, author = {Tender, Leonard M and Reimers, Clare E and Stecher, Hilmar A and Holmes, Dawn E and Bond, Daniel R and Lowy, Daniel A and Pilobello, Kanoelani and Fertig, Stephanie J and Lovley, Derek R} }