Use of a Coculture To Enable Current Production by Geobacter sulfurreducens

ABSTRACTMicrobial fuel cells often produce more electrical power with mixed cultures than with pure cultures. Here, we show that a coculture of a nonexoelectrogen (Escherichia coli) andGeobacter sulfurreducensimproved system performance relative to that of a pure culture of the exoelectrogen due to the consumption of oxygen leaking into the reactor.

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Strain- and Substrate-Dependent Redox Mediator and Electricity Production by Pseudomonas aeruginosa

Applied and Environmental Microbiology ◽

10.1128/aem.01342-16 ◽

2016 ◽

Vol 82 (16) ◽

pp. 5026-5038 ◽

Cited By ~ 21

Author(s):

Erick M. Bosire ◽

Lars M. Blank ◽

Miriam A. Rosenbaum

Keyword(s):

Pseudomonas Aeruginosa ◽

Electron Transfer ◽

Fuel Cells ◽

Microbial Fuel Cells ◽

Pure Culture ◽

Bioelectrochemical Systems ◽

Content Type ◽

Mediated Electron Transfer ◽

Phenazine Production ◽

Model Strain

ABSTRACTPseudomonas aeruginosais an important, thriving member of microbial communities of microbial bioelectrochemical systems (BES) through the production of versatile phenazine redox mediators. Pure culture experiments with a model strain revealed synergistic interactions ofP. aeruginosawith fermenting microorganisms whereby the synergism was mediated through the shared fermentation product 2,3-butanediol. Our work here shows that the behavior and efficiency ofP. aeruginosain mediated current production is strongly dependent on the strain ofP. aeruginosa. We compared levels of phenazine production by the previously investigated model strainP. aeruginosaPA14, the alternative model strainP. aeruginosaPAO1, and the BES isolatePseudomonassp. strain KRP1 with glucose and the fermentation products 2,3-butanediol and ethanol as carbon substrates. We found significant differences in substrate-dependent phenazine production and resulting anodic current generation for the three strains, with the BES isolate KRP1 being overall the best current producer and showing the highest electrochemical activity with glucose as a substrate (19 μA cm−2with ∼150 μg ml−1phenazine carboxylic acid as a redox mediator). Surprisingly,P. aeruginosaPAO1 showed very low phenazine production and electrochemical activity under all tested conditions.IMPORTANCEMicrobial fuel cells and other microbial bioelectrochemical systems hold great promise for environmental technologies such as wastewater treatment and bioremediation. While there is much emphasis on the development of materials and devices to realize such systems, the investigation and a deeper understanding of the underlying microbiology and ecology are lagging behind. Physiological investigations focus on microorganisms exhibiting direct electron transfer in pure culture systems. Meanwhile, mediated electron transfer with natural redox compounds produced by, for example,Pseudomonas aeruginosamight enable an entire microbial community to access a solid electrode as an alternative electron acceptor. To better understand the ecological relationships between mediator producers and mediator utilizers, we here present a comparison of the phenazine-dependent electroactivities of threePseudomonasstrains. This work forms the foundation for more complex coculture investigations of mediated electron transfer in microbial fuel cells.

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

mBio ◽

10.1128/mbio.00105-13 ◽

2013 ◽

Vol 4 (2) ◽

Cited By ~ 68

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.

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Complete Genome Sequence of Geobacter sulfurreducens Strain YM18, Isolated from River Sediment in Japan

Genome Announcements ◽

10.1128/genomea.00352-18 ◽

2018 ◽

Vol 6 (19) ◽

Author(s):

Kengo Inoue ◽

Yoshitoshi Ogura ◽

Yoshihiro Kawano ◽

Tetsuya Hayashi

Keyword(s):

Fuel Cells ◽

Genome Sequence ◽

Complete Genome Sequence ◽

Microbial Fuel Cells ◽

Complete Genome ◽

Dominant Species ◽

River Sediment ◽

Geobacter Sulfurreducens ◽

Bioelectrochemical System ◽

Content Type

ABSTRACT Geobacter sulfurreducens is known to be a dominant species in the anode biofilms of microbial fuel cells. Here, we report the complete genome sequence of G. sulfurreducens strain YM18. Strain YM18 was isolated from a biofilm formed on an anode poised at −400 mV (versus an Ag/AgCl electrode) in a bioelectrochemical system.

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

Applied and Environmental Microbiology ◽

10.1128/aem.02617-20 ◽

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.

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Electricity Production by Geobacter sulfurreducens Attached to Electrodes

Applied and Environmental Microbiology ◽

10.1128/aem.69.3.1548-1555.2003 ◽

2003 ◽

Vol 69 (3) ◽

pp. 1548-1555 ◽

Cited By ~ 1347

Author(s):

Daniel R. Bond ◽

Derek R. Lovley

Keyword(s):

Electron Transfer ◽

Fuel Cells ◽

Electron Donor ◽

Electron Acceptor ◽

Microbial Fuel Cells ◽

Electrical Current ◽

Geobacter Sulfurreducens ◽

Electricity Production ◽

Organic Substrates ◽

Current Production

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 μM), and hydrogen was metabolized to a threshold of 3 Pa. The rates of electron transfer to electrodes (0.21 to 1.2 μmol of electrons/mg of protein/min) were similar to those observed for respiration with Fe(III) citrate as the electron acceptor (Eo′ =+0.37 V). The production of current in microbial fuel cell (65 mA/m2 of electrode surface) or poised-potential (163 to 1,143 mA/m2) 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.

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Selection of a variant of Geobacter sulfurreducens with enhanced capacity for current production in microbial fuel cells

Biosensors and Bioelectronics ◽

10.1016/j.bios.2009.05.004 ◽

2009 ◽

Vol 24 (12) ◽

pp. 3498-3503 ◽

Cited By ~ 258

Author(s):

Hana Yi ◽

Kelly P. Nevin ◽

Byoung-Chan Kim ◽

Ashely E. Franks ◽

Anna Klimes ◽

...

Keyword(s):

Fuel Cells ◽

Microbial Fuel Cells ◽

Geobacter Sulfurreducens ◽

Current Production ◽

Selection Of

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Variations of electron flux and microbial community in air-cathode microbial fuel cells fed with different substrates

Water Science & Technology ◽

10.2166/wst.2012.240 ◽

2012 ◽

Vol 66 (4) ◽

pp. 748-753 ◽

Cited By ~ 15

Author(s):

Jaecheul Yu ◽

Younghyun Park ◽

Haein Cho ◽

Jieun Chun ◽

Jiyun Seon ◽

...

Keyword(s):

Fuel Cells ◽

Microbial Communities ◽

Microbial Fuel Cells ◽

Electricity Generation ◽

Electron Flow ◽

Batch Mode ◽

Electrochemically Active ◽

Oxidation Of Organic Compounds ◽

Current Production ◽

Electron Sink

Microbial fuel cells (MFCs) can convert chemical energy to electricity using microbes as catalysts and a variety of organic wastewaters as substrates. However, electron loss occurs when fermentable substrates are used because fermentation bacteria and methanogens are involved in electron flow from the substrates to electricity. In this study, MFCs using glucose (G-MFC), propionate (P-MFC), butyrate (B-MFC), acetate (A-MFC), and a mix (M-MFC, glucose:propionate:butyrate:acetate = 1:1:1:1) were operated in batch mode. The metabolites and microbial communities were analyzed. The current was the largest electron sink in M-, G-, B-, and A-MFCs; the initial chemical oxygen demands (CODini) involved in current production were 60.1% for M-MFC, 52.7% for G-MFC, 56.1% for B-MFC, and 68.3% for A-MFC. Most of the glucose was converted to propionate (40.6% of CODini) and acetate (21.4% of CODini) through lactate (80.3% of CODini) and butyrate (6.1% of CODini). However, an unknown source (62.0% of CODini) and the current (34.5% of CODini) were the largest and second-largest electron sinks in P-MFC. Methane gas was only detected at levels of more than 10% in G- and M-MFCs, meaning that electrochemically active bacteria (EAB) could out-compete acetoclastic methanogens. The microbial communities were different for fermentable and non-fermentable substrate-fed MFCs. Probably, bacteria related to Lactococcus spp. found in G-MFCs with fermentable substrates would be involved in both fermentation and electricity generation. Acinetobacter-like species, and Rhodobacter-like species detected in all the MFCs would be involved in oxidation of organic compounds and electricity generation.

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Rumen Inoculum Enhances Cathode Performance in Single-Chamber Air-Cathode Microbial Fuel Cells

Materials ◽

10.3390/ma15010379 ◽

2022 ◽

Vol 15 (1) ◽

pp. 379

Author(s):

Ignacio T. Vargas ◽

Natalia Tapia ◽

John M. Regan

Keyword(s):

Fuel Cells ◽

Microbial Fuel Cells ◽

Rumen Fluid ◽

Oxygen Demand ◽

Air Cathode ◽

Single Chamber ◽

Higher Power ◽

Mixed Microbial Community ◽

Current Production ◽

Soluble Chemical Oxygen Demand

During the last decade, bioprospecting for electrochemically active bacteria has included the search for new sources of inoculum for microbial fuel cells (MFCs). However, concerning power and current production, a Geobacter-dominated mixed microbial community derived from a wastewater inoculum remains the standard. On the other hand, cathode performance is still one of the main limitations for MFCs, and the enrichment of a beneficial cathodic biofilm emerges as an alternative to increase its performance. Glucose-fed air-cathode reactors inoculated with a rumen-fluid enrichment and wastewater showed higher power densities and soluble chemical oxygen demand (sCOD) removal (Pmax = 824.5 mWm−2; ΔsCOD = 96.1%) than reactors inoculated only with wastewater (Pmax = 634.1 mWm−2; ΔsCOD = 91.7%). Identical anode but different cathode potentials suggest that differences in performance were due to the cathode. Pyrosequencing analysis showed no significant differences between the anodic community structures derived from both inocula but increased relative abundances of Azoarcus and Victivallis species in the cathodic rumen enrichment. Results suggest that this rarely used inoculum for single-chamber MFCs contributed to cathodic biofilm improvements with no anodic biofilm effects.

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