scholarly journals Long-range electron transport in Geobacter sulfurreducens biofilms is redox gradient-driven

2012 ◽  
Vol 109 (38) ◽  
pp. 15467-15472 ◽  
Author(s):  
Rachel M. Snider ◽  
Sarah M. Strycharz-Glaven ◽  
Stanislav D. Tsoi ◽  
Jeffrey S. Erickson ◽  
Leonard M. Tender
Keyword(s):  
Electron Transport ◽  
Long Range ◽  
Redox Status ◽  
Electron Source ◽  
Oxidation Potential ◽  
Geobacter Sulfurreducens ◽  
The Other ◽  
Anode Surface ◽  
Extracellular Electron Transfer ◽  
Oxidation Potentials

Geobacter spp. can acquire energy by coupling intracellular oxidation of organic matter with extracellular electron transfer to an anode (an electrode poised at a metabolically oxidizing potential), forming a biofilm extending many cell lengths away from the anode surface. It has been proposed that long-range electron transport in such biofilms occurs through a network of bound redox cofactors, thought to involve extracellular matrix c-type cytochromes, as occurs for polymers containing discrete redox moieties. Here, we report measurements of electron transport in actively respiring Geobacter sulfurreducens wild type biofilms using interdigitated microelectrode arrays. Measurements when one electrode is used as an anode and the other electrode is used to monitor redox status of the biofilm 15 μm away indicate the presence of an intrabiofilm redox gradient, in which the concentration of electrons residing within the proposed redox cofactor network is higher farther from the anode surface. The magnitude of the redox gradient seems to correlate with current, which is consistent with electron transport from cells in the biofilm to the anode, where electrons effectively diffuse from areas of high to low concentration, hopping between redox cofactors. Comparison with gate measurements, when one electrode is used as an electron source and the other electrode is used as an electron drain, suggests that there are multiple types of redox cofactors in Geobacter biofilms spanning a range in oxidation potential that can engage in electron transport. The majority of these redox cofactors, however, seem to have oxidation potentials too negative to be involved in electron transport when acetate is the electron source.

scholarly journals Direct Observation of Electrically Conductive Pili Emanating from Geobacter sulfurreducens

2021 ◽  
Author(s):  
Xinying Liu ◽  
David Jeffrey Fraser Walker ◽  
Stephen Nonnenmann ◽  
Dezhi Sun ◽  
Derek R. Lovley
Keyword(s):  
Electron Transfer ◽  
Electron Transport ◽  
Long Range ◽  
Geobacter Sulfurreducens ◽  
Metal Corrosion ◽  
Extracellular Electron Transfer ◽  
Wild Type ◽  
Electrically Conductive ◽  
In The Wild ◽  
Pilin Gene

Geobacter sulfurreducens is a model microbe for elucidating the mechanisms for extracellular electron transfer in several biogeochemical cycles, bioelectrochemical applications, and microbial metal corrosion. Multiple lines of evidence previously suggested that electrically conductive pili (e-pili) are an essential conduit for long-range extracellular electron transport in G. sulfurreducens. However, it has recently been reported that G. sulfurreducens does not express e-pili and that filaments comprised of multi-heme c-type cytochromes are responsible for long-range electron transport. This possibility was directly investigated by examining cells, rather than filament preparations, with atomic force microscopy. Approximately 90 % of the filaments emanating from wild-type cells had a diameter (3 nm) and conductance consistent with previous reports of e-pili harvested from G. sulfurreducens or heterologously expressed in E. coli from the G. sulfurreducens pilin gene. The remaining 10% of filaments had a morphology consistent with filaments comprised of the c-type cytochrome OmcS. A strain expressing a modified pilin gene designed to yield poorly conductive pili expressed 90 % filaments with a 3 nm diameter, but greatly reduced conductance, further indicating that the 3 nm diameter conductive filaments in the wild-type strain were e-pili. A strain in which genes for five of the most abundant outer-surface c-type cytochromes, including OmcS, was deleted yielded only 3 nm diameter filaments with the same conductance as in the wild-type. These results demonstrate that e-pili are the most abundant conductive filaments expressed by G. sulfurreducens, consistent with previous functional studies demonstrating the need for e-pili for long-range extracellular electron transfer.

scholarly journals Cytochrome OmcS is not essential for long-range electron transport in Geobacter sulfurreducens strain KN400

2020 ◽  
Author(s):  
David J. F. Walker ◽  
Yang Li ◽  
David Meier ◽  
Samantha Pinches ◽  
Dawn E. Holmes ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Electron Transport ◽  
Long Range ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Electrically Conductive ◽  
Closely Related Species ◽  
Direct Interspecies Electron Transfer ◽  
Interspecies Electron Transfer ◽  
Extracellular Electron Transport

AbstractThe multi-heme c-type cytochrome OmcS, is one of the central components for extracellular electron transport in Geobacter sulfurreducens strain DL-1, but its role in other microbes, including other strains of G. sulfurreducens is currently a matter of debate. Therefore, we investigated the function of OmcS in G. sulfurreducens strain KN400, which is even more effective in extracellular electron transfer than strain DL-1. We found that deleting omcS from strain KN400 did not negatively impact the rate of Fe(III) oxide reduction and did not affect the strain’s ability to accept electrons via direct interspecies electron transfer. The OmcS-deficient strain also continued to produce conductive filaments, consistent with the concept that electrically conductive pili are the primary conduit for long-range electron transfer in G. sulfurreducens and closely related species. These findings, coupled with the lack of OmcS homologs in most other microbes capable of extracellular electron transfer, suggest that OmcS is not a common critical component for extracellular electron transfer.

scholarly journals Aromatic Amino Acids Required for Pili Conductivity and Long-Range Extracellular Electron Transport in Geobacter sulfurreducens

mBio ◽  
2013 ◽  
Vol 4 (2) ◽  
Author(s):  
Madeline Vargas ◽  
Nikhil S. Malvankar ◽  
Pier-Luc Tremblay ◽  
Ching Leang ◽  
Jessica A. Smith ◽  
...  
Keyword(s):  
Amino Acids ◽  
Electron Transport ◽  
Long Range ◽  
Microbial Fuel Cells ◽  
Aromatic Amino Acids ◽  
Geobacter Sulfurreducens ◽  
Control Strain ◽  
Content Type ◽  
Current Production ◽  
Extracellular Electron Transport

ABSTRACTIt has been proposed thatGeobacter sulfurreducensrequires 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 ofG. 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 whichG. sulfurreducensPilA 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 multihemec-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 ofG. sulfurreducensmust be conductive in order for the cells to be effective in extracellular long-range electron transport.IMPORTANCEExtracellular electron transfer byGeobacterspecies 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, andGeobacterorganisms are often abundant in such environments.Geobacter sulfurreducensproduces 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 ofG. sulfurreducensthat produces pili with low conductivity is limited in these extracellular electron transport functions provides further insight into these environmentally significant processes.

Long-range electron transport to Fe(III) oxide via pili with metallic-like conductivity

2012 ◽  
Vol 40 (6) ◽  
pp. 1186-1190 ◽  
Author(s):  
Derek R. Lovley
Keyword(s):  
Electron Transport ◽  
Long Range ◽  
Geobacter Sulfurreducens ◽  
Oxide Reduction ◽  
Electron Hopping ◽  
Electrically Conductive ◽  
Electron Conduction ◽  
Geobacter Species ◽  
Redox Active

The mechanisms for Fe(III) oxide reduction by Geobacter species are of interest because Geobacter species have been shown to play an important role in Fe(III) oxide reduction in a diversity of environments in which Fe(III) reduction is a geochemically significant process. Geobacter species specifically express pili during growth on Fe(III) oxide compared with growth on soluble chelated Fe(III), and mutants that cannot produce pili are unable to effectively reduce Fe(III) oxide. The pili of Geobacter sulfurreducens are electrically conductive along their length under physiologically relevant conditions and exhibit a metallic-like conductivity similar to that observed previously in synthetic organic metals. Metallic-like conductivity in a biological protein filament is a previously unrecognized mechanism for electron transport that differs significantly from the more well-known biological strategy of electron hopping/tunnelling between closely spaced redox-active proteins. The multihaem c-type cytochrome OmcS is specifically associated with pili and is necessary for Fe(III) oxide reduction. However, multiple lines of evidence, including the metallic-like conductivity of the pili and the fact that OmcS molecules are spaced too far apart for electron hopping/tunnelling, indicate that OmcS is not responsible for long-range electron conduction along the pili. The role of OmcS may be to facilitate electron transfer from the pili to Fe(III) oxide. Long-range electron transport via pili with metallic-like conductivity is a paradigm shift that has important implications not only for Fe(III) oxide reduction, but also for interspecies electron exchange in syntrophic microbial communities as well as microbe–electrode interactions and the emerging field of bioelectronics.

Thermally activated long range electron transport in living biofilms

2015 ◽  
Vol 17 (48) ◽  
pp. 32564-32570 ◽  
Author(s):  
Matthew D. Yates ◽  
Joel P. Golden ◽  
Jared Roy ◽  
Sarah M. Strycharz-Glaven ◽  
Stanislav Tsoi ◽  
...  
Keyword(s):  
Electron Transport ◽  
Long Range ◽  
Geobacter Sulfurreducens ◽  
Electron Hopping ◽  
Thermally Activated ◽  
Conductivity Electron ◽  
Extracellular Electron Transport ◽  
Conductive Surfaces

The rate of extracellular electron transport through living, electrode-grown Geobacter sulfurreducens biofilms decreases with decreasing temperature, consistent with incoherent redox conductivity (electron hopping) among hemes of c-type cytochromes to conductive surfaces.

scholarly journals Direct Observation of Electrically Conductive Pili Emanating from Geobacter sulfurreducens

mBio ◽  
2021 ◽  
Vol 12 (4) ◽  
Author(s):  
Xinying Liu ◽  
David J. F. Walker ◽  
Stephen S. Nonnenmann ◽  
Dezhi Sun ◽  
Derek R. Lovley
Keyword(s):  
Electron Transport ◽  
Environmental Impacts ◽  
Long Range ◽  
Direct Observation ◽  
Geobacter Sulfurreducens ◽  
Electrically Conductive ◽  
Metal Cofactors

Electroactive microbes have significant environmental impacts, as well as applications in bioenergy and bioremediation. The composition, function, and even existence of electrically conductive pili (e-pili) has been one of the most contentious areas of investigation in electromicrobiology, in part because e-pili offer a mechanism for long-range electron transport that does not involve the metal cofactors common in much of biological electron transport.

scholarly journals Improper Localization of the OmcS Cytochrome May Explain the Inability of thexapD-Deficient Mutant ofGeobacter sulfurreducensto Reduce Fe(III) Oxide

2017 ◽  
Author(s):  
Kelly A. Flanagan ◽  
Ching Leang ◽  
Joy E. Ward ◽  
Derek R. Lovley
Keyword(s):  
Electron Transfer ◽  
Electron Transport ◽  
Type Strain ◽  
Wild Type Strain ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Outer Cell ◽  
Wild Type ◽  
Redox Active ◽  
In The Wild

AbstractExtracellular electron transfer through a redox-active exopolysaccharide matrix has been proposed as a strategy for extracellular electron transfer to Fe(III) oxide byGeobacter sulfurreducens,based on the phenotype of axapD-deficient strain. Central to this model was the assertion that thexapD-deficient strain produced pili decorated with the multi-hemec-type cytochrome OmcS in manner similar to the wild-type strain. Further examination of thexapD-deficient strain with immunogold labeling of OmcS and transmission electron microscopy revealed that OmcS was associated with the outer cell surface rather than pili. PilA, the pilus monomer, could not be detected in thexapD-deficient strain under conditions in which it was readily detected in the wild-type strain. Multiple lines of evidence in previous studies have suggested that long-range electron transport to Fe(III) oxides proceeds through electrically conductive pili and that OmcS associated with the pili is necessary for electron transfer from the pili to Fe(III) oxides. Therefore, an alternative explanation for the Fe(III) oxide reduction phenotype of thexapD-deficientstrain is that the pili-OmcS route for extracellular electron transport to Fe(III) oxide has been disrupted in thexapD-deficient strain.

scholarly journals Aromatic Amino Acids Required for Pili Conductivity and Long-Range Extracellular Electron Transport in Geobacter sulfurreducens

mBio ◽  
2013 ◽  
Vol 4 (2) ◽  
Author(s):  
Madeline Vargas ◽  
Nikhil S. Malvankar ◽  
Pier-Luc Tremblay ◽  
Ching Leang ◽  
Jessica A. Smith ◽  
...  
Keyword(s):  
Amino Acids ◽  
Electron Transport ◽  
Long Range ◽  
Aromatic Amino Acids ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transport

Effects of Doping on the Electrochemical and Electrical Properties of Poly(2,5-di(2-thienyl)pyrrole)

1999 ◽  
Vol 64 (8) ◽  
pp. 1357-1368 ◽  
Author(s):  
Enric Brillas ◽  
José Carrasco ◽  
Ramon Oliver ◽  
Francesc Estrany ◽  
Víctor Ruiz
Keyword(s):  
Mass Spectrometry ◽  
Fast Atom Bombardment ◽  
Oxidation Potential ◽  
Ethanolic Solution ◽  
Pt Electrode ◽  
Reversible Process ◽  
Oxidation Potentials ◽  
Lower Productivity ◽  
Polymeric Chains ◽  
Linear Molecules

The electropolymerization of 2,5-di(2-(thienyl)pyrrole) (SNS) on a Pt electrode from ethanolic solution with LiClO4 or LiCl as electrolyte has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). In both media, a quasi-reversible process has been indicated by CV, reversing the scan at low oxidation potentials. Under these conditions, reducible positive charges formed in both oxidized polymers are compensated by the entrance of anions from solution. Elemental analysis reveals that polymers generated at a low oxidation potential by CA contain a 21.03% (w/w) of ClO4- or a 9.56% (w/w) of Cl-. The poly(SNS) doped with Cl- presents higher proportion of reducible positive charges, higher polymerization charge and lower productivity. A much higher electrical conductivity, however, has been found for the poly(SNS) doped with ClO4-. Both polymers are soluble in DMSO, acetone and methanol. The dimer, trimer, tetramer and pentamer have been detected as soluble and neutral linear oligomers by mass spectrometry-fast atom bombardment. The analysis of polymers by infrared spectroscopy confirms the predominant formation of linear molecules with α-α linkages between monomeric units. A condensation mechanism involving one-electron oxidation of all electrogenerated linear and neutral polymeric chains is proposed to explain the SNS electropolymerization.

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