<i>Shewanella</i>
            secretes flavins that mediate extracellular electron transfer

Marsili, Enrico; Baron, Daniel; Shikhare, Indraneel D.; Coursolle, Dan; Gralnick, Jeffrey A.; Bond, Daniel R.

doi:10.1073/pnas.0710525105

Cited by 1,706 publications

(1,624 citation statements)

References 44 publications

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“…Oxygen enhanced anodic current production during phase 1 (SI, Figure S2a), probably due to the higher energy obtained by MR-1 during complete lactate oxidation under aerated conditions 34,35 . A thicker biofilm that could be visually observed in this instance and a presumably higher production of redox mediators which exhibited (anodic) current onsets at potentials similar to the midpoint potentials of flavins 22 (Figure S3), are also possible reasons for this enhanced performance.…”

Section: Resultsmentioning

confidence: 80%

Enhanced Performance of Hexavalent Chromium Reducing Cathodes in the Presence ofShewanella oneidensisMR-1 and Lactate

Xafenias

Zhang

Banks

2013

Environ. Sci. Technol.

134

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Biocathodes for the reduction of the highly toxic hexavalent chromium (Cr(VI)) were investigated using Shewanella oneidensis MR-1 (MR-1) as a bio-catalyst and performance was assessed in terms of current production and Cr(VI) reduction. Potentiostatically controlled experiments (-500 mV vs. Ag/AgCl) showed that a mediatorless MR-1 biocathode started up 2 under aerated conditions in the presence of lactate, received 5.5 and 1.7 times more electrons for Cr(VI) reduction over a 4-hour operating period than controls without lactate and with lactate but without MR-1, respectively. Cr(VI) reduction was also enhanced, with a decrease in concentration over the 4-h operating period of 9 mg/L Cr(VI), compared to only 1 and 3 mg/L respectively in the controls. Riboflavin, an electron shuttle mediator naturally produced by MR-1, was also found to have a positive impact in potentiostatically controlled cathodes. Additionally, a microbial fuel cell (MFC) with MR-1 and lactate present in both anode and cathode produced a maximum current density of 32.5 mA/m 2 (1,000 Ω external load) after receiving a 10 mg/L Cr(VI) addition in the cathode, and cathodic efficiency increased steadily over an 8-day operation period with successive Cr(VI) additions. In conclusion, effective and continuous Cr(VI) reduction with associated current production were achieved when MR-1 and lactate were both present in the biocathodes. INTRODUCTIONHexavalent chromium (Cr(VI)) is a highly toxic, mutagenic and carcinogenic substance that is present in the effluent streams of a wide range of industrial processes, including electroplating, leather tanning and wood preserving 1 . It is highly soluble and, because of its long history of use and often its disposal after inappropriate or no treatment, it has become one of the most abundant inorganic contaminants in groundwater. Ideally Cr(VI) should be removed from groundwater in the natural environment, and because of the inherent dangers to health the stringent guideline limit of 50 μg/L has been issued for total chromium concentration in drinking water 1,2 . Removal options include ion-exchange, adsorption and electrodialysis 3 ; however in many of these applications chromium keeps its toxic hexavalent state. Reduction of Cr(VI) to the considerably 3 less toxic trivalent form Cr(III) and its subsequent precipitation at neutral pH could be considered a more effective remediation strategy 4 .A possible method for Cr(VI) reduction using a microbial fuel cell (MFC) has recently been proposed, where Cr(VI) was used as an oxidant in the cathode to generate an electrical energy output 5,6 . At low pH values where H + is abundant, cathodic Cr(VI) reduction has been demonstrated at relatively fast rates and without the use of a catalyst 5,6 . In the neutral pH region, however, the reaction kinetics are slower due to low H + availability:CrO 4 2-+ 8H + + 3e -= Cr 3+ + 4H 2 O (1) At neutral pH, Cr(VI) reduction takes place under lower cathode potentials and is also severely inhibited by Cr(III) oxyhydroxide monolayers w...

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Section: Resultsmentioning

confidence: 80%

Enhanced Performance of Hexavalent Chromium Reducing Cathodes in the Presence ofShewanella oneidensisMR-1 and Lactate

Xafenias

Zhang

Banks

2013

Environ. Sci. Technol.

134

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“…Recently, flavins were proposed to be soluble mediators in extracellular electron transfer to Fe(III) oxides and to anodes of MFCs [22,23]. To determine if these mediators contributed to the differences in current output by wild type and mutant strains, we measured flavin levels in culture supernatants at the end of the MFC experiments (210 h).…”

Section: Role Of Riboflavins In Extracellular Electron Transfer In Pimentioning

confidence: 99%

“…6). If reduction of riboflavins was the predominant mechanism used for electron transfer [22], all strains would be expected to produce similar amounts of current, due to limiting concentrations of the riboflavin mediator. The presence of riboflavin in all culture supernatants would suggest that the ability to perform indirect (mediated) electron transfer exists at equal probabilities for all mutants.…”

Section: Role Of Riboflavins In Extracellular Electron Transfer In Pimentioning

confidence: 99%

The Role of Shewanella oneidensis MR‐1 Outer Surface Structures in Extracellular Electron Transfer

et al. 2010

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The ability of the metal reducer Shewanella oneidensis MR-1 to generate electricity in microbial fuel cells (MFCs) depends on the activity of a predicted type IV prepilin peptidase; PilD. Analysis of an S. oneidensis MR-1 pilD mutant indicated that it was deficient in pili production (Msh and type IV) and type II secretion (T2S). The requirement for T2S in metal reduction has been previously identified, but the role of pili remains largely unexplored. To define the role of type IV or Msh pili in electron transfer, mutants that lack one or both pilus biogenesis systems were generated and analyzed; a mutant that lacked flagella was also constructed and tested. All mutants were able to reduce insoluble Fe(III) and to generate current in MFCs, in contrast to the T2S mutant that is deficient in both processes. Our results show that loss of metal reduction in a PilD mutant is due to a T2S deficiency, and therefore the absence of c cytochromes from the outer surface of MR-1 cells, and not the loss of pili or flagella. Furthermore, MR-1 mutants deficient in type IV pili or flagella generated more current than the wild type, even though extracellular riboflavin levels were similar in all strains. This enhanced current generating ability is in contrast to a mutant that lacks the outer membrane c cytochromes, MtrC and OmcA. This mutant generated significantly less current than the wild type in an MFC and was unable to reduce Fe(III). These results indicated that although nanofilaments and soluble mediators may play a role in electron transfer, surface exposure of outer membrane c cytochromes was the determining factor in extracellular electron transfer in S. oneidensis MR-1.

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“…Three decades ago, EET was discovered as manganese and iron respiration in species of Geobacter and Shewanella (Lovley and Phillips, 1988; Lovley, 1991; Marsili et al ., 2008a). More than 90 species have been reported to perform EET (Koch and Harnisch, 2017) including the EET model organisms Geobacter sulfurreducens and Shewanella oneidensis .…”

Section: Introductionmentioning

confidence: 99%

Towards patterned bioelectronics: facilitated immobilization of exoelectrogenic Escherichia coli with heterologous pili

Lienemann

TerAvest

Pitkänen

et al. 2018

Microbial Biotechnology

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SummaryBiosensors detect signals using biological sensing components such as redox enzymes and biological cells. Although cellular versatility can be beneficial for different applications, limited stability and efficiency in signal transduction at electrode surfaces represent a challenge. Recent studies have shown that the Mtr electron conduit from Shewanella oneidensis MR‐1 can be produced in Escherichia coli to generate an exoelectrogenic model system with well‐characterized genetic tools. However, means to specifically immobilize this organism at solid substrates as electroactive biofilms have not been tested previously. Here, we show that mannose‐binding Fim pili can be produced in exoelectrogenic E. coli and can be used to selectively attach cells to a mannose‐coated material. Importantly, cells expressing fim genes retained current production by the heterologous Mtr electron conduit. Our results demonstrate the versatility of the exoelectrogenic E. coli system and motivate future work that aims to produce patterned biofilms for bioelectronic devices that can respond to various biochemical signals.

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Shewanella secretes flavins that mediate extracellular electron transfer

Cited by 1,706 publications

References 44 publications

Enhanced Performance of Hexavalent Chromium Reducing Cathodes in the Presence ofShewanella oneidensisMR-1 and Lactate

Enhanced Performance of Hexavalent Chromium Reducing Cathodes in the Presence ofShewanella oneidensisMR-1 and Lactate

The Role of Shewanella oneidensis MR‐1 Outer Surface Structures in Extracellular Electron Transfer

Towards patterned bioelectronics: facilitated immobilization of exoelectrogenic Escherichia coli with heterologous pili

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