scholarly journals The electrically conductive pili of Geobacter soli

2020 ◽  
Author(s):  
Shiyan Zhuo ◽  
Guiqin Yang ◽  
Li Zhuang
Keyword(s):  
Electron Transfer ◽  
Outer Surface ◽  
Electronic Materials ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Oxide Reduction ◽  
Electrically Conductive ◽  
Current Production ◽  
Current Densities ◽  
Pilin Gene

AbstractElectrically conductive pili (e-pili) enable electron transport over multiple cell lengths to extracellular environments and play an important role in extracellular electron transfer (EET) of Geobacter species. To date, the studies of e-pili have mainly focused on Geobacter sulfurreducens and the closely related Geobacter metallireducens because of their developed genetic manipulation systems. We investigated the role of G. soli pili in EET by directly deleting the pilin gene, pilA, which is predicted to encode e-pili. Deletion of pilA, prevented the production of pili, resulting in poor Fe(III) oxide reduction and low current production, implying that G. soli pili is required for EET. To further evaluate the conductivity of G. soli pili compared with G. sulfurreducens pili, the pilA of G. soli was heterologously expressed in G. sulfurreducens, yielding the G. sulfurreducens strain GSP. This strain produced abundant pili with similar conductivity to the control strain that expressed native G. sulfurreducens pili, consistent with G. soli as determined by direct measurement, which suggested that G. soli pili is electrically conductive. Surprisingly, strain GSP was deficient in Fe(III) oxide reduction and current production due to the impaired content of outer-surface c-type cytochromes. These results demonstrated that heterologous pili of G. sulfurreducens severely reduces the content of outer-surface c-type cytochromes and consequently eliminates the capacity for EET, which strongly suggests an attention should be paid to the content of c-type cytochromes when employing G. sulfurreducens to heterologously express pili from other microorganisms.IMPORTANCEThe studies of electrically conductive pili (e-pili) of Geobacter species are of interest because of its application prospects in electronic materials. e-Pili are considered a substitution for electronic materials due to its renewability, biodegradability and robustness. Continued exploration of additional e-pili of Geobacter soli will improve the understanding of their biological role in extracellular electron transfer and expand the range of available electronic materials. Heterologously expressing the pilin genes from phylogenetically diverse microorganisms has been proposed as an emerging approach to screen potential e-pili according to high current densities. However, our results indicated that a Geobacter sulfurreducens strain heterologously expressing a pilin gene produced low current densities that resulted from a lack of content of c-type cytochromes, which were likely to possess e-pili. These results provide referential significance to yield e-pili from diverse microorganisms.

scholarly journals Unexpected Genomic Features of High Current Density-Producing Geobacter sulfurreducens strain YM18

2021 ◽  
Author(s):  
Takashi Fujikawa ◽  
Yoshitoshi Ogura ◽  
Koki Ishigami ◽  
Yoshihiro Kawano ◽  
Miyuki Nagamine ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Current Density ◽  
Iron Reduction ◽  
High Current Density ◽  
Model Organism ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
High Current ◽  
Current Production ◽  
Current Densities

Abstract Geobacter sulfurreducens produces high current densities and it has been used as a model organism for extracellular electron transfer studies. Nine G. sulfurreducens strains were isolated from biofilms formed on an anode poised at –0.2 V (vs. SHE) in a bioelectrochemical system in which river sediment was used as an inoculum. The maximum current density of an isolate, strain YM18 (9.29 A/m2), was higher than that of the strains PCA (5.72 A/m2), the type strain of G. sulfurreducens, and comparable to strain KN400 (8.38 A/m2), which is another high current producing strain of G. sulfurreducens. Genomic comparison of strains PCA, KN400, and YM18 revealed that omcB, xapD, spc, and ompJ, which are known to be important genes for iron reduction and current production in PCA, were not present in YM18. In the PCA and KN400 genomes, two and one region (s) encoding CRISPR/Cas systems were identified, respectively, but they were missing in the YM18 genome. These results indicate that there is genetic variation in the key components involved in extracellular electron transfer among G. sulfurreducens strains.

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 Electrically Conductive Pili from Pilin Genes of Phylogenetically Diverse Microorganisms

2017 ◽  
Author(s):  
David J.F. Walker ◽  
Ramesh Y. Adhikari ◽  
Dawn E. Holmes ◽  
Joy E. Ward ◽  
Trevor L. Woodard ◽  
...  
Keyword(s):  
Amino Acids ◽  
Phylogenetic Diversity ◽  
Electronic Materials ◽  
Aromatic Amino Acids ◽  
Geobacter Sulfurreducens ◽  
High Current ◽  
Electrically Conductive ◽  
Simple Method ◽  
Current Densities ◽  
Pilin Gene

AbstractThe possibility that bacteria other than Geobacter species might contain genes for electrically conductive pili (e-pili) was investigated by heterologously expressing pilin genes of interest in Geobacter sulfurreducens. Strains of G. sulfurreducens producing high current densities, which are only possible with e-pili, were obtained with pilin genes from Flexistipes sinusarabici, Calditerrivibrio nitroreducens, and Desulfurivibrio alkaliphilus. The conductance of pili from these strains was comparable to native G. sulfurreducens e-pili. The e-pili derived from C. nitroreducens, and D. alkaliphilus pilin genes are the first examples of relatively long (> 100 amino acids) pilin monomers assembling into e-pili. The pilin gene from Desulfofervidus auxilii did not yield e-pili, suggesting that the hypothesis that this sulfate reducer wires itself to ANME-1 microbes with e-pili to promote anaerobic methane oxidation should be reevaluated. A high density of aromatic amino acids and a lack of substantial aromatic-free gaps along the length of long pilins may be important characteristics leading to e-pili. This study demonstrates a simple method to screen pilin genes from difficult-to-culture microorganisms for their potential to yield e-pili; reveals new potential sources for biologically based electronic materials; and suggests that a wide phylogenetic diversity of microorganisms may employ e-pili for extracellular electron exchange.

scholarly journals Biofilm and Nanowire Production Leads to Increased Current in Geobacter sulfurreducens Fuel Cells

2006 ◽  
Vol 72 (11) ◽  
pp. 7345-7348 ◽  
Author(s):  
Gemma Reguera ◽  
Kelly P. Nevin ◽  
Julie S. Nicoll ◽  
Sean F. Covalla ◽  
Trevor L. Woodard ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Energy Efficient ◽  
Geobacter Sulfurreducens ◽  
Electricity Production ◽  
Anode Surface ◽  
Efficient Manner ◽  
Electrically Conductive ◽  
Genetic Studies ◽  
Electronic Network ◽  
Current Production

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.

scholarly journals Outer Cell Surface Components Essential for Fe(III) Oxide Reduction by Geobacter metallireducens

2012 ◽  
Vol 79 (3) ◽  
pp. 901-907 ◽  
Author(s):  
Jessica A. Smith ◽  
Derek R. Lovley ◽  
Pier-Luc Tremblay
Keyword(s):  
Outer Surface ◽  
Surface Protein ◽  
Transcript Abundance ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Outer Cell ◽  
Gene Transcript ◽  
Oxide Reduction ◽  
Geobacter Metallireducens ◽  
Content Type

ABSTRACTGeobacterspecies are important Fe(III) reducers in a diversity of soils and sediments. Mechanisms for Fe(III) oxide reduction have been studied in detail inGeobacter sulfurreducens, but a number of the most thoroughly studied outer surface components ofG. sulfurreducens, particularlyc-type cytochromes, are not well conserved amongGeobacterspecies. In order to identify cellular components potentially important for Fe(III) oxide reduction inGeobacter metallireducens, gene transcript abundance was compared in cells grown on Fe(III) oxide or soluble Fe(III) citrate with whole-genome microarrays. Outer-surface cytochromes were also identified. Deletion of genes forc-type cytochromes that had higher transcript abundance during growth on Fe(III) oxides and/or were detected in the outer-surface protein fraction identified sixc-type cytochrome genes, that when deleted removed the capacity for Fe(III) oxide reduction. Several of thec-type cytochromes which were essential for Fe(III) oxide reduction inG. metallireducenshave homologs inG. sulfurreducensthat are not important for Fe(III) oxide reduction. Other genes essential for Fe(III) oxide reduction included a gene predicted to encode an NHL (Ncl-1–HT2A–Lin-41) repeat-containing protein and a gene potentially involved in pili glycosylation. Genes associated with flagellum-based motility, chemotaxis, and pili had higher transcript abundance during growth on Fe(III) oxide, consistent with the previously proposed importance of these components in Fe(III) oxide reduction. These results demonstrate that there are similarities in extracellular electron transfer betweenG. metallireducensandG. sulfurreducensbut the outer-surfacec-type cytochromes involved in Fe(III) oxide reduction are different.

scholarly journals A Geobacter sulfurreducens Strain Expressing Pseudomonas aeruginosa Type IV Pili Localizes OmcS on Pili but Is Deficient in Fe(III) Oxide Reduction and Current Production

2013 ◽  
Vol 80 (3) ◽  
pp. 1219-1224 ◽  
Author(s):  
Xing Liu ◽  
Pier-Luc Tremblay ◽  
Nikhil S. Malvankar ◽  
Kelly P. Nevin ◽  
Derek R. Lovley ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Electron Transfer ◽  
Structural Features ◽  
Geobacter Sulfurreducens ◽  
Control Strain ◽  
Oxide Reduction ◽  
Content Type ◽  
Type Iv ◽  
Current Production ◽  
Pilin Protein

ABSTRACTThe conductive pili ofGeobacterspecies play an important role in electron transfer to Fe(III) oxides, in long-range electron transport through current-producing biofilms, and in direct interspecies electron transfer. Although multiple lines of evidence have indicated that the pili ofGeobacter sulfurreducenshave a metal-like conductivity, independent of the presence ofc-type cytochromes, this claim is still controversial. In order to further investigate this phenomenon, a strain ofG. sulfurreducens, designated strain PA, was constructed in which the gene for the native PilA, the structural pilin protein, was replaced with the PilA gene ofPseudomonas aeruginosaPAO1. Strain PA expressed and properly assembledP. aeruginosaPilA subunits into pili and exhibited a profile of outer surfacec-type cytochromes similar to that of a control strain expressing theG. sulfurreducensPilA. Surprisingly, the strain PA pili were decorated with thec-type cytochrome OmcS in a manner similar to the control strain. However, the strain PA pili were 14-fold less conductive than the pili of the control strain, and strain PA was severely impaired in Fe(III) oxide reduction and current production. These results demonstrate that the presence of OmcS on pili is not sufficient to confer conductivity to pili and suggest that there are unique structural features of theG. sulfurreducensPilA that are necessary for conductivity.

scholarly journals Generation of High Current Densities in Geobacter sulfurreducens Lacking the Putative Gene for the PilB Pilus Assembly Motor

2021 ◽  
Author(s):  
Toshiyuki Ueki ◽  
David J. F. Walker ◽  
Kelly P. Nevin ◽  
Joy E. Ward ◽  
Trevor L. Woodard ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Geobacter Sulfurreducens ◽  
Metal Corrosion ◽  
Extracellular Electron Transfer ◽  
Renewable Electricity ◽  
Gene Deletions ◽  
Putative Gene ◽  
Content Type ◽  
Soils And Sediments ◽  
Current Densities

Geobacter sulfurreducens is a model microbe for the study of biogeochemically and technologically significant processes, such as the reduction of Fe(III) oxides in soils and sediments, bioelectrochemical applications that produce electric current from waste organic matter or drive useful processes with the consumption of renewable electricity, direct interspecies electron transfer in anaerobic digestors and methanogenic soils and sediments, and metal corrosion. Elucidating the phenotypes associated with gene deletions is an important strategy for determining the mechanisms for extracellular electron transfer in G. sulfurreducens .

scholarly journals Proteolytic maturation of the Outer Membrane c-type cytochrome OmcZ by Subtilisin-like Serine Protease is Essential for Optimal Current Production by Geobacter sulfurreducens

2021 ◽  
Author(s):  
Ayako Kai ◽  
Takahiro Tokuishi ◽  
Takashi Fujikawa ◽  
Yoshihiro Kawano ◽  
Toshiyuki Ueki ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Fuel Cells ◽  
Outer Membrane ◽  
Microbial Fuel Cells ◽  
Culture Supernatant ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Mature Form ◽  
Optimal Current ◽  
Current Production

An outer membrane c-type cytochrome (OmcZ) in Geobacter sulfurreducens is essential for optimal current production in microbial fuel cells. OmcZ exists in two forms, small and large, designated as OmcZS and OmcZL, respectively. However, it is still not known how these two structures are formed. A disruption mutant of the GSU2075 gene encoding a subtilisin-like serine protease (designated as ozpA for the OmcZ protease), which is located downstream of omcZ, produced low currents at a level similar to that of the omcZ-deficient mutant strain. Biochemical analyses revealed that the ozpA mutant accumulated OmcZL and did not produce OmcZS, which is thought to be a mature form that is essential for the extracellular electron transfer to the electrode. A heterologous expression system cell lysate from an Escherichia coli strain producing OzpA cleaved OmcZL and generated OmcZS as the proteolytic product. Among culture supernatant, loosely-bound outer surface, and intracellular protein fractions from wild-type G. sulfurreducens, only culture supernatant protein fraction showed the OmcZL cleavage activity, indicating the the mature form of OmcZ, OmcZS, can be produced outside the cells. These results indicate that OzpA is an essential protease for current production via the maturation of OmcZ, and OmcZS is the key to the extracellular electron transfer to electrodes. This proteolytic maturation of OmcZ is a unique regulation among known c-type cytochromes in G. sulfurreducens. IMPORTANCE Microbial fuel cells are a promising technology for energy generation from various waste types. However, the molecular mechanisms of microbial extracellular electron transfer to the electrode need to be elucidated. G. sulfurreducens is a commonly key player in electricity generation in mixed-culture microbial fuel cell systems and a model microorganism for study of extracellular electron transfer. Outer membrane c-type cytochrome OmcZ is essential for an optimal current production by G. sulfurreducens. OmcZ proteolytic cleavage occurs during maturation, but the underlying mechanism is unknown. This study identifies a subtilisin-like protease OzpA, which plays a role in cleaving OmcZ and generating the mature form of OmcZ (OmcZS). OzpA is essential for current production, and thus, the proteolytic maturation of OmcZ. This is a novel regulation of the c-type cytochrome for G. sulfurreducens extracellular electron transfer. This study also provide new insights into the design strategy and development of microbial extracellular electron transfer for an efficient energy conversion from chemical energy to electricity.

scholarly journals Generation of High Current Densities by Pure Cultures of Anode-Respiring Geoalkalibacter spp. under Alkaline and Saline Conditions in Microbial Electrochemical Cells

mBio ◽  
2013 ◽  
Vol 4 (3) ◽  
Author(s):  
Jonathan P. Badalamenti ◽  
Rosa Krajmalnik-Brown ◽  
César I. Torres
Keyword(s):  
Electron Transfer ◽  
Geobacter Sulfurreducens ◽  
Extracellular Electron Transfer ◽  
Electrochemical Cells ◽  
Organic Substrates ◽  
High Current ◽  
Content Type ◽  
Pure Cultures ◽  
Current Densities ◽  
Anode Respiring Bacteria

ABSTRACTAnode-respiring bacteria (ARB) generate electric current in microbial electrochemical cells (MXCs) by channeling electrons from the oxidation of organic substrates to an electrode. Production of high current densities by monocultures in MXCs has resulted almost exclusively from the activity ofGeobacter sulfurreducens, a neutrophilic freshwater Fe(III)-reducing bacterium and the highest-current-producing member documented for theGeobacteraceaefamily of theDeltaproteobacteria. Here we report high current densities generated by haloalkaliphilicGeoalkalibacterspp., thus broadening the capability for high anode respiration rates by including other genera within theGeobacteraceae. In this study, acetate-fed pure cultures of two relatedGeoalkalibacterspp. produced current densities of 5.0 to 8.3 and 2.4 to 3.3 A m−2under alkaline (pH 9.3) and saline (1.7% NaCl) conditions, respectively. Chronoamperometric studies of halophilicGlk. subterraneusDSM 23483 and alkaliphilicGlk. ferrihydriticusDSM 17813 suggested that cells performed long-range electron transfer through electrode-attached biofilms and not through soluble electron shuttles.Glk. ferrihydriticusalso oxidized ethanol directly to produce current, with maximum current densities of 5.7 to 7.1 A m−2and coulombic efficiencies of 84 to 95%. Cyclic voltammetry (CV) elicited a sigmoidal response with characteristic onset, midpoint, and saturation potentials, while CV performed in the absence of an electron donor suggested the involvement of redox molecules in the biofilm that were limited by diffusion. These results matched those previously reported for actively respiringGb. sulfurreducensbiofilms producing similar current densities (~5 to 9 A m−2).IMPORTANCEThis study establishes the highest current densities ever achieved by pure cultures of anode-respiring bacteria (ARB) under alkaline and saline conditions in microbial electrochemical cells (MXCs) and provides the first electrochemical characterization of the genusGeoalkalibacter. Production of high current densities among theGeobacteraceaeis no longer exclusive toGeobacter sulfurreducens, suggesting greater versatility for this family in fundamental and applied microbial electrochemical cell (MXC) research than previously considered. Additionally, this work raises the possibility that different members of theGeobacteraceaehave conserved molecular mechanisms governing respiratory extracellular electron transfer to electrodes. Thus, the capacity for high current generation may exist in other uncultivated members of this family. Advancement of MXC technology for practical uses must rely on an expanded suite of ARB capable of using different electron donors and producing high current densities under various conditions.Geoalkalibacterspp. can potentially broaden the practical capabilities of MXCs to include energy generation and waste treatment under expanded ranges of salinity and pH.

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.

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