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Derek R. Lovley - One of the best experts on this subject based on the ideXlab platform.
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toward establishing minimum requirements for extracellular electron transfer in Geobacter Sulfurreducens
Fems Microbiology Letters, 2017Co-Authors: Toshiyuki Ueki, Laurie N Didonato, Derek R. LovleyAbstract:The highly redundant pathways for extracellular electron transfer in Geobacter Sulfurreducens must be simplified for this microorganism to serve as an effective chassis for applications such as the development of sensors and biocomputing. Five homologs of the periplasmic c-type cytochromes, PpcA-E, offer the possibility of multiple routes of electron transfer across the periplasm. The presence of a large number of outer membrane c-type cytochromes allows G. Sulfurreducens to adapt to disruption of an electron transfer pathway in the outer membrane. A strain in which genes for all five periplasmic cytochromes, PpcA-E, were deleted did not reduce Fe(III). Introducing ppcA under the control of an IPTG-inducible system in the quintuple deletion strain yielded a strain that reduced Fe(III) only in the presence of IPTG. A strain lacking known major outer membrane cytochromes, OmcB, OmcE, OmcS and OmcT, and putative functional homologs of OmcB, did not reduce Fe(III). Introduction of omcB in this septuple deletion strain restored the ability to reduce Fe(III). These results demonstrate that it is possible to trim redundancy from the extracellular electron transfer pathways in G. Sulfurreducens in order to construct strains with defined extracellular electron transfer routes.
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proteome of Geobacter Sulfurreducens in the presence of u vi
Microbiology, 2014Co-Authors: Roberto Orellana, Tunde Mester, Manju L Sharma, Kim K Hixson, Sean Murphy, Mary S Lipton, Derek R. LovleyAbstract:Geobacter species often play an important role in the in situ bioremediation of uranium-contaminated groundwater, but little is known about how these microbes avoid uranium toxicity. To evaluate this further, the proteome of Geobacter Sulfurreducens exposed to 100 µM U(VI) acetate was compared to control cells not exposed to U(VI). Of the 1363 proteins detected from these cultures, 203 proteins had higher abundance during exposure to U(VI) compared with the control cells and 148 proteins had lower abundance. U(VI)-exposed cultures expressed lower levels of proteins involved in growth, protein and amino acid biosynthesis, as well as key central metabolism enzymes as a result of the deleterious effect of U(VI) on the growth of G. Sulfurreducens. In contrast, proteins involved in detoxification, such as several efflux pumps belonging to the RND (resistance–nodulation–cell division) family, and membrane protection, and other proteins, such as chaperones and proteins involved in secretion systems, were found in higher abundance in cells exposed to U(VI). Exposing G. Sulfurreducens to U(VI) resulted in a higher abundance of many proteins associated with the oxidative stress response, such as superoxide dismutase and superoxide reductase. A strain in which the gene for superoxide dismutase was deleted grew more slowly than the WT strain in the presence of U(VI), but not in its absence. The results suggested that there is no specific mechanism for uranium detoxification. Rather, multiple general stress responses are induced, which presumably enable Geobacter species to tolerate high uranium concentrations.
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engineering Geobacter Sulfurreducens to produce a highly cohesive conductive matrix with enhanced capacity for current production
Energy and Environmental Science, 2013Co-Authors: Ching Leang, Ashley E. Franks, Kelly P Nevin, Nikhil S Malvankar, Derek R. LovleyAbstract:The conductive biofilms of Geobacter Sulfurreducens have potential applications in renewable energy, bioremediation, and bioelectronics. In an attempt to alter biofilm properties, genes encoding proteins with a PilZ domain were deleted from the G. Sulfurreducens genome. A strain, in which the gene GSU1240 was deleted, designated strain CL-1, formed biofilms much more effectively than did the wild-type strain. Increased production of pili and exopolysaccharide were associated with the enhanced biofilm production. When grown with an electrode as the electron acceptor CL-1 produced biofilms that were 6-fold more conductive than wild-type biofilms. The greater conductivity lowered the potential losses in microbial fuel cells, decreasing the charge transfer resistance at the biofilm–anode surface by ca. 60% and lowering the formal potential by 50 mV. These lower potential losses increased the potential energy of electrons reaching the biofilm–anode interface and enabled strain CL-1 to produce 70% higher power densities than the wild-type strain. Current-producing biofilms were highly cohesive and could be peeled off graphite electrodes intact, yielding a novel conductive biological material. This study demonstrates that simple genetic manipulation can yield improved bioelectronics materials with energy applications.
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aromatic amino acids required for pili conductivity and long range extracellular electron transport in Geobacter Sulfurreducens
Mbio, 2013Co-Authors: Ching Leang, Kelly P Nevin, Pier-luc Tremblay, Nikhil S Malvankar, Madeline Vargas, Jessica A Smith, Pranav Patel, Oona Synoeyenboswest, Derek R. LovleyAbstract: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 thefive 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 deco- rated 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's. These results demonstrate that the pili of G. Sulfurreducens must be conductive in order for the cells to be effective in extracellu- lar long-range electron transport. IMPORTANCE Extracellular electron transfer by Geobacterspecies plays an important role in the biogeochemistry of soils and sed- iments and has a number of bioenergy applications. For example, microbial reduction of Fe(III) oxide is one of the most geo- chemically significant processes in anaerobic soils, aquatic sediments, and aquifers, and Geobacterorganisms 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 wastewa- ter 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.
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comparative genomic analysis of Geobacter Sulfurreducens kn400 a strain with enhanced capacity for extracellular electron transfer and electricity production
BMC Genomics, 2012Co-Authors: Jessica E Butler, Muktak Aklujkar, Nelson D Young, Derek R. LovleyAbstract:Background A new strain of Geobacter Sulfurreducens, strain KN400, produces more electrical current in microbial fuel cells and reduces insoluble Fe(III) oxides much faster than the wildtype strain, PCA. The genome of KN400 was compared to wildtype with the goal of discovering how the network for extracellular electron transfer has changed and how these two strains evolved.
Gemma Reguera - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic stratification in electroactive biofilms of Geobacter Sulfurreducens mediated by pilus nanowires
Nature Communications, 2016Co-Authors: Rebecca J. Steidl, Sanela Lampa-pastirk, Gemma RegueraAbstract:Electricity generation by Geobacter Sulfurreducens biofilms grown on electrodes involves matrix-associated electron carriers, such as c -type cytochromes. Yet, the contribution of the biofilm’s conductive pili remains uncertain, largely because pili-defective mutants also have cytochrome defects. Here we report that a pili-deficient mutant carrying an inactivating mutation in the pilus assembly motor PilB has no measurable defects in cytochrome expression, yet forms anode biofilms with reduced electroactivity and is unable to grow beyond a threshold distance (∼10 μm) from the underlying electrode. The defects are similar to those of a Tyr3 mutant, which produces poorly conductive pili. The results support a model in which the conductive pili permeate the biofilms to wire the cells to the conductive biofilm matrix and the underlying electrode, operating coordinately with cytochromes until the biofilm reaches a threshold thickness that limits the efficiency of the cytochrome pathway but not the functioning of the conductive pili network. The roles played by cytochromes and conductive filamentous appendages (pili) in the electrical conductivity of Geobacter bacterial biofilms are controversial. Here, Steidl et al . present evidence that both mechanisms cooperate in thin biofilms, while pili are important for conductivity across thicker biofilms.
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mechanistic stratification in electroactive biofilms of Geobacter Sulfurreducens mediated by pilus nanowires
Nature Communications, 2016Co-Authors: Rebecca J. Steidl, Sanela Lampapastirk, Gemma RegueraAbstract:Electricity generation by Geobacter Sulfurreducens biofilms grown on electrodes involves matrix-associated electron carriers, such as c-type cytochromes. Yet, the contribution of the biofilm's conductive pili remains uncertain, largely because pili-defective mutants also have cytochrome defects. Here we report that a pili-deficient mutant carrying an inactivating mutation in the pilus assembly motor PilB has no measurable defects in cytochrome expression, yet forms anode biofilms with reduced electroactivity and is unable to grow beyond a threshold distance (∼10 μm) from the underlying electrode. The defects are similar to those of a Tyr3 mutant, which produces poorly conductive pili. The results support a model in which the conductive pili permeate the biofilms to wire the cells to the conductive biofilm matrix and the underlying electrode, operating coordinately with cytochromes until the biofilm reaches a threshold thickness that limits the efficiency of the cytochrome pathway but not the functioning of the conductive pili network.
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structural and functional insights into the conductive pili of Geobacter Sulfurreducens revealed in molecular dynamics simulations
Physical Chemistry Chemical Physics, 2015Co-Authors: Gustavo Troiano Feliciano, Rebecca J. Steidl, Gemma RegueraAbstract:Geobacter Sulfurreducens (GS) electronically connects with extracellular electron acceptors using conductive protein filaments or pili. To gain insights into their role as biological nanowires, we investigated the structural dynamics of the GS pilus in solution via molecular dynamics simulations. In the model, all of the pilin's aromatics clustered as a right-handed helical band along the pilus, maintaining inter-aromatic distances and dimer configurations optimal for multistep hopping. The aromatics were interspersed within the regions of highest negative potential, which influenced the type and configuration of the aromatic contacts and the rates of electron transfer. Small foci of positive potential were also present but were neutralized within uncharged regions, thus minimizing charge trapping. Consistent with the model predictions, mutant strains with reduced aromatic contacts or negative potentials had defects in pili functions such as the reduction of Fe(III) oxides and electrodes. The results therefore support the notion of a pilus fiber evolved to function as an electronic conduit between the cell and extracellular electron acceptors.
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molecular and electronic structure of the peptide subunit of Geobacter Sulfurreducens conductive pili from first principles
Journal of Physical Chemistry A, 2012Co-Authors: Gustavo Troiano Feliciano, Gemma Reguera, Antonio J R Da Silva, Emilio ArtachoAbstract:The respiration of metal oxides by the bacterium Geobacter Sulfurreducens requires the assembly of a small peptide (the GS pilin) into conductive filaments termed pili. We gained insights into the contribution of the GS pilin to the pilus conductivity by developing a homology model and performing molecular dynamics simulations of the pilin peptide in vacuo and in solution. The results were consistent with a predominantly helical peptide containing the conserved α-helix region required for pilin assembly but carrying a short carboxy-terminal random-coiled segment rather than the large globular head of other bacterial pilins. The electronic structure of the pilin was also explored from first principles and revealed a biphasic charge distribution along the pilin and a low electronic HOMO–LUMO gap, even in a wet environment. The low electronic band gap was the result of strong electrostatic fields generated by the alignment of the peptide bond dipoles in the pilin’s α-helix and by charges from ions in solutio...
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electron donors supporting growth and electroactivity of Geobacter Sulfurreducens anode biofilms
Applied and Environmental Microbiology, 2012Co-Authors: Allison M Speers, Gemma RegueraAbstract:Geobacter bacteria efficiently oxidize acetate into electricity in bioelectrochemical systems, yet the range of fermentation products that support the growth of anode biofilms and electricity production has not been thoroughly investigated. Here, we show that Geobacter Sulfurreducens oxidized formate and lactate with electrodes and Fe(III) as terminal electron acceptors, though with reduced efficiency compared to acetate. The structure of the formate and lactate biofilms increased in roughness, and the substratum coverage decreased, to alleviate the metabolic constraints derived from the assimilation of carbon from the substrates. Low levels of acetate promoted formate carbon assimilation and biofilm growth and increased the system's performance to levels comparable to those with acetate only. Lactate carbon assimilation also limited biofilm growth and led to the partial oxidization of lactate to acetate. However, lactate was fully oxidized in the presence of fumarate, which redirected carbon fluxes into the tricarboxylic acid (TCA) cycle, and by acetate-grown biofilms. These results expand the known ranges of electron donors for Geobacter-driven fuel cells and identify microbial constraints that can be targeted to develop better-performing strains and increase the performance of bioelectrochemical systems.
Alain Bergel - One of the best experts on this subject based on the ideXlab platform.
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The open circuit potential of Geobacter Sulfurreducens bioanodes depends on the electrochemical adaptation of the strain
Electrochemistry Communications, 2013Co-Authors: Laurence Soussan, Benjamin Erable, Marie-line Délia, Alain BergelAbstract:Bioanodes for acetate oxidation were formed with pure cultures of Geobacter Sulfurreducens under constant polarization potential. With the original commercial strain, the bioanodes formed at + 0.2 V/SCE exhibited open circuit potential (OCP) of 0.0 V/SCE, while the bioanodes formed at − 0.2 V/SCE had OCP around − 0.52 V/SCE. In contrast, the bioanodes formed with bacterial cells collected from a previous current-producing bioanode exhibited OCP of − 0.52 V/SCE whatever the polarization potential used to form them (+ 0.2 V/SCE or − 0.2 V/SCE). The "electrochemically-adapted strain" kept its electrochemical characteristics after successive cultures in solution. High steady-state currents were reached (16-19 A m- 2) in all cases without any dependence on strain adaptation or applied potential.
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Electrochemical reduction of CO2 catalysed by Geobacter Sulfurreducens grown on polarized stainless steel cathodes
Electrochemistry Communications, 2013Co-Authors: Laurence Soussan, Benjamin Erable, Marie-line Délia, Julien Riess, Alain BergelAbstract:Polarized stainless steel cathodes in pure cultures of Geobacter Sulfurreducens generated reduction currents of up to 30 A/m2 even when the sole electron acceptor contained in solution was completely reduced. It was shown here that these currents were driven by the carbon dioxide that was provided to the solution. It was postulated that CO2 reduction consumed succinate and produced glycerol, which remained stored inside the cells and was released under the effect of stress.
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effect of Geobacter Sulfurreducens on the microbial corrosion of mild steel ferritic and austenitic stainless steels
Corrosion Science, 2009Co-Authors: Maha Mehanna, Régine Basséguy, Marie-line Délia, Alain BergelAbstract:Abstract The influence of Geobacter Sulfurreducens was tested on the anaerobic corrosion of four different steels: mild steel 1145, ferritic steel 403 and austenitic steels 304L and 316L. Within a few hours, the presence of cells induced a free potential (Eoc) ennoblement around +0.3 V on 1145 mild steel, 403 ferritic steel and 304L austenitic steels and slightly less on 316L. The kinetics of Eoc ennoblement depended on the amount of bacteria in the inoculum, but the final potential value depended essentially on the nature of the material. This effect was due to the capacity of G. Sulfurreducens to create a direct cathodic reaction on steel surfaces, extracting the electrons directly from material. The presence of bacterial cells modified the corrosion features of mild steel and ferritic steel, so that corrosion attacks were gathered in determined zones of the surface. Local corrosion was significantly enhanced on ferritic steel. Potential ennoblement was not sufficient to induce corrosion on austenitic steels. In contrast G. Sulfurreducens delayed the occurrence of pitting on 304L steel because of its capability to oxidize acetate at high potential values. The electrochemical behaviour of 304L steel was not affected by the concentration of soluble electron donor (acetate, 1–10 mM) or the amount of planktonic cells; it was directly linked to the biofilm coverage. After polarization pitting curves had been recorded, microscopic observations showed that pits propagated only in the surface zones where cell settlement was the densest. The study evidenced that Geobacter Sulfurreducens can control the electrochemical behaviour of steels in complex ways that can lead to severe corrosion. As Geobacteraceae are ubiquitous species in sediments and soils they should now be considered as possible crucial actors in the microbial corrosion of buried equipment.
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Electrochemical activity of Geobacter Sulfurreducens biofilms on stainless steel anodes
Electrochimica Acta, 2008Co-Authors: Claire Dumas, Régine Basséguy, Alain BergelAbstract:Stainless steel was studied as anode for the biocatalysis of acetate oxidation by biofilms of Geobacter Sulfurreducens. Electrodes were individually polarized at different potential in the range −0.20V to +0.20V vs. Ag/AgCl either in the same reactor or in different reactors containing acetate as electron donor and no electron acceptor except the working electrode. At +0.20V vs. Ag/AgCl, the current increased after a 2-day lag period up to maximum current densities around 0.7Am−2 and 2.4Am−2 with 5mM and 10mM acetate, respectively. No current was obtained during chronoamperometry (CA) at potential values lower than 0.00V vs. Ag/AgCl, while the cyclic voltammetries (CV) that were performed periodically always detected a fast electron transfer, with the oxidation starting around −0.25V vs. Ag/AgCl. Epifluorescent microscopy showed that the current recorded by chronoamperometry was linked to the biofilm growth on the electrode surface, while CVs were more likely linked to the cells initially adsorbed from the inoculum. A model was proposed to explain the electrochemical behaviour of the biofilm, which appeared to be controlled by the pioneering adherent cells playing the role of “electrochemical gate” between the biofilm and the electrode surface.
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Microbial electrocatalysis with Geobacter Sulfurreducens biofilm on stainless steel cathodes
Electrochimica Acta, 2008Co-Authors: Claire Dumas, Régine Basséguy, Alain BergelAbstract:Stainless steel and graphite electrodes were individually addressed and polarized at -0.60 V vs. Ag/AgCl in reactors filled with a growth medium that contained 25 mM fumarate as the electron acceptor and no electron donor, in order to force the microbial cells to use the electrode as electron source. When the reactor was inoculated with Geobacter Sulfurreducens, the current increased and stabilized at average values around 0.75 A m(-2) for graphite and 20.5 A m(-2) for stainless steel. Cyclic voltammetry performed at the end of the experiment indicated that the reduction started at around -0.30 V vs. Ag/AgCl on stainless steel. Removing the biofilm formed on the electrode surface made the current totally disappear, confirming that the G. sit Sulfurreducens biofilm was fully responsible for the electrocatalysis of fumarate reduction. Similar current densities were recorded when the electrodes were polarized after being kept in open circuit for several days. The reasons for the bacteria presence and survival on non-connected stainless steel coupons were discussed. Chronoamperometry experiments performed at different potential values suggested that the biofilm-driven catalysis was controlled by electrochemical kinetics. The high current density obtained, quite close to the redox potential of the fumarate/succinate couple, presents stainless steel as a remarkable material to support biocathodes.
Ching Leang - One of the best experts on this subject based on the ideXlab platform.
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u vi reduction by diverse outer surface c type cytochromes of Geobacter Sulfurreducens
Applied and Environmental Microbiology, 2013Co-Authors: Roberto Orellana, Ching Leang, Mounir Izallalen, Janet J Leavitt, Luis R Comolli, Roseann Csencsits, Noemie Janot, Kelly A Flanagan, Arianna S Gray, Tunde MesterAbstract:Early studies with Geobacter Sulfurreducens suggested that outer-surface c-type cytochromes might play a role in U(VI) reduction, but it has recently been suggested that there is substantial U(VI) reduction at the surface of the electrically conductive pili known as microbial nanowires. This phenomenon was further investigated. A strain of G. Sulfurreducens, known as Aro-5, which produces pili with substantially reduced conductivity reduced U(VI) nearly as well as the wild type, as did a strain in which the gene for PilA, the structural pilin protein, was deleted. In order to reduce rates of U(VI) reduction to levels less than 20% of the wild-type rates, it was necessary to delete the genes for the five most abundant outer surface c-type cytochromes of G. Sulfurreducens. X-ray absorption near-edge structure spectroscopy demonstrated that whereas 83% ± 10% of the uranium associated with wild-type cells correspond to U(IV) after 4 h of incubation, with the quintuple mutant, 89% ± 10% of uranium was U(VI). Transmission electron microscopy and X-ray energy dispersion spectroscopy revealed that wild-type cells did not precipitate uranium along pili as previously reported, but U(IV) was precipitated at the outer cell surface. These findings are consistent with those of previous studies, which have suggested that G. Sulfurreducens requires outer-surface c-type cytochromes but not pili for the reduction of soluble extracellular electron acceptors.
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engineering Geobacter Sulfurreducens to produce a highly cohesive conductive matrix with enhanced capacity for current production
Energy and Environmental Science, 2013Co-Authors: Ching Leang, Ashley E. Franks, Kelly P Nevin, Nikhil S Malvankar, Derek R. LovleyAbstract:The conductive biofilms of Geobacter Sulfurreducens have potential applications in renewable energy, bioremediation, and bioelectronics. In an attempt to alter biofilm properties, genes encoding proteins with a PilZ domain were deleted from the G. Sulfurreducens genome. A strain, in which the gene GSU1240 was deleted, designated strain CL-1, formed biofilms much more effectively than did the wild-type strain. Increased production of pili and exopolysaccharide were associated with the enhanced biofilm production. When grown with an electrode as the electron acceptor CL-1 produced biofilms that were 6-fold more conductive than wild-type biofilms. The greater conductivity lowered the potential losses in microbial fuel cells, decreasing the charge transfer resistance at the biofilm–anode surface by ca. 60% and lowering the formal potential by 50 mV. These lower potential losses increased the potential energy of electrons reaching the biofilm–anode interface and enabled strain CL-1 to produce 70% higher power densities than the wild-type strain. Current-producing biofilms were highly cohesive and could be peeled off graphite electrodes intact, yielding a novel conductive biological material. This study demonstrates that simple genetic manipulation can yield improved bioelectronics materials with energy applications.
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aromatic amino acids required for pili conductivity and long range extracellular electron transport in Geobacter Sulfurreducens
Mbio, 2013Co-Authors: Ching Leang, Kelly P Nevin, Pier-luc Tremblay, Nikhil S Malvankar, Madeline Vargas, Jessica A Smith, Pranav Patel, Oona Synoeyenboswest, Derek R. LovleyAbstract: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 thefive 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 deco- rated 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's. These results demonstrate that the pili of G. Sulfurreducens must be conductive in order for the cells to be effective in extracellu- lar long-range electron transport. IMPORTANCE Extracellular electron transfer by Geobacterspecies plays an important role in the biogeochemistry of soils and sed- iments and has a number of bioenergy applications. For example, microbial reduction of Fe(III) oxide is one of the most geo- chemically significant processes in anaerobic soils, aquatic sediments, and aquifers, and Geobacterorganisms 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 wastewa- ter 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.
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alignment of the c type cytochrome omcs along pili of Geobacter Sulfurreducens
Applied and Environmental Microbiology, 2010Co-Authors: Ching Leang, Xinlei Qian, Tunde Mester, Derek R. LovleyAbstract:Immunogold localization revealed that OmcS, a cytochrome that is required for Fe(III) oxide reduction by Geobacter Sulfurreducens, was localized along the pili. The apparent spacing between OmcS molecules suggests that OmcS facilitates electron transfer from pili to Fe(III) oxides rather than promoting electron conduction along the length of the pili.
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Genome-wide analysis of the RpoN regulon in Geobacter Sulfurreducens
BMC Genomics, 2009Co-Authors: Ching Leang, Katy Juárez, Raymond J. Didonato, Toshiyuki Ueki, Gemma Reguera, Cinthia Núñez, Marko Puljic, Julia Krushkal, Bradley L. PostierAbstract:Background The role of the RNA polymerase sigma factor RpoN in regulation of gene expression in Geobacter Sulfurreducens was investigated to better understand transcriptional regulatory networks as part of an effort to develop regulatory modules for genome-scale in silico models, which can predict the physiological responses of Geobacter species during groundwater bioremediation or electricity production.
Kelly P Nevin - One of the best experts on this subject based on the ideXlab platform.
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engineering Geobacter Sulfurreducens to produce a highly cohesive conductive matrix with enhanced capacity for current production
Energy and Environmental Science, 2013Co-Authors: Ching Leang, Ashley E. Franks, Kelly P Nevin, Nikhil S Malvankar, Derek R. LovleyAbstract:The conductive biofilms of Geobacter Sulfurreducens have potential applications in renewable energy, bioremediation, and bioelectronics. In an attempt to alter biofilm properties, genes encoding proteins with a PilZ domain were deleted from the G. Sulfurreducens genome. A strain, in which the gene GSU1240 was deleted, designated strain CL-1, formed biofilms much more effectively than did the wild-type strain. Increased production of pili and exopolysaccharide were associated with the enhanced biofilm production. When grown with an electrode as the electron acceptor CL-1 produced biofilms that were 6-fold more conductive than wild-type biofilms. The greater conductivity lowered the potential losses in microbial fuel cells, decreasing the charge transfer resistance at the biofilm–anode surface by ca. 60% and lowering the formal potential by 50 mV. These lower potential losses increased the potential energy of electrons reaching the biofilm–anode interface and enabled strain CL-1 to produce 70% higher power densities than the wild-type strain. Current-producing biofilms were highly cohesive and could be peeled off graphite electrodes intact, yielding a novel conductive biological material. This study demonstrates that simple genetic manipulation can yield improved bioelectronics materials with energy applications.
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aromatic amino acids required for pili conductivity and long range extracellular electron transport in Geobacter Sulfurreducens
Mbio, 2013Co-Authors: Ching Leang, Kelly P Nevin, Pier-luc Tremblay, Nikhil S Malvankar, Madeline Vargas, Jessica A Smith, Pranav Patel, Oona Synoeyenboswest, Derek R. LovleyAbstract: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 thefive 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 deco- rated 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's. These results demonstrate that the pili of G. Sulfurreducens must be conductive in order for the cells to be effective in extracellu- lar long-range electron transport. IMPORTANCE Extracellular electron transfer by Geobacterspecies plays an important role in the biogeochemistry of soils and sed- iments and has a number of bioenergy applications. For example, microbial reduction of Fe(III) oxide is one of the most geo- chemically significant processes in anaerobic soils, aquatic sediments, and aquifers, and Geobacterorganisms 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 wastewa- ter 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.
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anaerobes unleashed aerobic fuel cells of Geobacter Sulfurreducens
Journal of Power Sources, 2011Co-Authors: Kelly P Nevin, Ashley E. Franks, Trevor L Woodard, Pei Zhang, Derek R. LovleyAbstract:Abstract One of the limitations of power generation with microbial fuel cells is that the anode must typically be maintained under anaerobic conditions. When oxygen is present in the anode chamber microorganisms oxidize the fuel with the reduction of oxygen rather than electron transfer to the anode. A system in which fuel is provided from within a graphite anode and diffuses out to the outer surface of the anode was designed to overcome these limitations. A biofilm of Geobacter Sulfurreducens strain KN400, pregrown on the surface of a graphite electrode in a traditional two-chambered system with an anaerobic anode chamber and acetate as an external fuel source, produced current just as well under aerobic conditions when acetate was provided via diffusion from an internal concentrated acetate solution. No acetate was detectable in the external medium. In contrast, aerobic systems in which acetate was provided in the external medium completely failed within 48 h. Internally fed anodes colonized by a strain of KN400 adapted to grow at marine salinities produced current in aerobic seawater as well as an anaerobic anode system. The ability to generate current with an anode under aerobic conditions increases the potential applications and design options for microbial fuel cells.
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Microtoming coupled to microarray analysis to evaluate the spatial metabolic status of Geobacter Sulfurreducens biofilms
The ISME Journal, 2010Co-Authors: Ashley E. Franks, Richard H. Glaven, Kelly P Nevin, Derek R. LovleyAbstract: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 μm from anode surface) and outer (30–60 μm) fractions. Transcriptional analysis revealed that, at a twofold threshold, 146 genes had significant ( P
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pilr a transcriptional regulator for pilin and other genes required for fe iii reduction in Geobacter Sulfurreducens
Journal of Molecular Microbiology and Biotechnology, 2009Co-Authors: Katy Juárez, Byoung Chan Kim, Gemma Reguera, Kelly P Nevin, Derek R. Lovley, Leticia Olvera, Barbara A. MethéAbstract:Growth using Fe(III) as a terminal electron acceptor is a critical physiological process in Geobacter Sulfurreducens . However, the mechanisms of electron transfer during Fe(III) red