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Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply

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Abstract
Background: Microbial electrosynthesis is a novel approach that aims at shifting the cellular metabolism towards electron-dense target products by extracellular electron supply. Many organisms including several acetogenic bacteria have been shown to be able to consume electrical current. However, suitable hosts for relevant industrial processes are yet to be discovered, and major knowledge gaps about the underlying fundamental processes still remain. Results: In this paper, we present the first report of electron uptake by the Gram-positive, ethanol-producing acetogen, Clostridium autoethanogenum. Under heterotrophic conditions, extracellular electron supply induced a significant metabolic shift away from acetate. In electrically enhanced fermentations on fructose, acetate production was cut by more than half, while production of lactate and 2,3-butanediol increased by 35-fold and threefold, respectively. The use of mediators with different redox potential revealed a direct dependency of the metabolic effect on the redox potential at which electrons are supplied. Only electrons delivered at a redox potential low enough to reduce ferredoxin caused the reported effect. Conclusions: Production in acetogenic organisms is usually challenged by cellular energy limitations if the target product does not lead to a net energy gain as in the case of acetate. The presented results demonstrate a significant shift of carbon fluxes away from acetate towards the products, lactate and 2,3-butanediol, induced by small electricity input (similar to 0.09 mol of electrons per mol of substrate). This presents a simple and attractive method to optimize acetogenic fermentations for production of chemicals and fuels using electrochemical techniques. The relationship between metabolic shift and redox potential of electron feed gives an indication of possible electron-transfer mechanisms and helps to prioritize further research efforts.
Keywords
Microbial electrosynthesis, Bio production, Gas fermentation, Wood-Ljungdahl pathway, Extracellular electron transport, Redox mediator, Acetogen, Rnf complex, MICROBIAL ELECTROSYNTHESIS, COMMODITY CHEMICALS, CARBON-DIOXIDE, FUELS, ELECTRICITY, FERMENTATION, IMPROVEMENT, ACETOGEN, ETHANOL, SYNGAS

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Chicago
Kracke, Frauke, Bernardino Virdis, Paul V Bernhardt, Korneel Rabaey, and Jens O Kromer. 2016. “Redox Dependent Metabolic Shift in Clostridium Autoethanogenum by Extracellular Electron Supply.” Biotechnology for Biofuels 9.
APA
Kracke, F., Virdis, B., Bernhardt, P. V., Rabaey, K., & Kromer, J. O. (2016). Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply. BIOTECHNOLOGY FOR BIOFUELS, 9.
Vancouver
1.
Kracke F, Virdis B, Bernhardt PV, Rabaey K, Kromer JO. Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply. BIOTECHNOLOGY FOR BIOFUELS. 2016;9.
MLA
Kracke, Frauke, Bernardino Virdis, Paul V Bernhardt, et al. “Redox Dependent Metabolic Shift in Clostridium Autoethanogenum by Extracellular Electron Supply.” BIOTECHNOLOGY FOR BIOFUELS 9 (2016): n. pag. Print.
@article{8511551,
  abstract     = {Background: Microbial electrosynthesis is a novel approach that aims at shifting the cellular metabolism towards electron-dense target products by extracellular electron supply. Many organisms including several acetogenic bacteria have been shown to be able to consume electrical current. However, suitable hosts for relevant industrial processes are yet to be discovered, and major knowledge gaps about the underlying fundamental processes still remain. 
Results: In this paper, we present the first report of electron uptake by the Gram-positive, ethanol-producing acetogen, Clostridium autoethanogenum. Under heterotrophic conditions, extracellular electron supply induced a significant metabolic shift away from acetate. In electrically enhanced fermentations on fructose, acetate production was cut by more than half, while production of lactate and 2,3-butanediol increased by 35-fold and threefold, respectively. The use of mediators with different redox potential revealed a direct dependency of the metabolic effect on the redox potential at which electrons are supplied. Only electrons delivered at a redox potential low enough to reduce ferredoxin caused the reported effect. 
Conclusions: Production in acetogenic organisms is usually challenged by cellular energy limitations if the target product does not lead to a net energy gain as in the case of acetate. The presented results demonstrate a significant shift of carbon fluxes away from acetate towards the products, lactate and 2,3-butanediol, induced by small electricity input (similar to 0.09 mol of electrons per mol of substrate). This presents a simple and attractive method to optimize acetogenic fermentations for production of chemicals and fuels using electrochemical techniques. The relationship between metabolic shift and redox potential of electron feed gives an indication of possible electron-transfer mechanisms and helps to prioritize further research efforts.},
  articleno    = {249},
  author       = {Kracke, Frauke and Virdis, Bernardino and Bernhardt, Paul V and Rabaey, Korneel and Kromer, Jens O},
  issn         = {1754-6834},
  journal      = {BIOTECHNOLOGY FOR BIOFUELS},
  keyword      = {Microbial electrosynthesis,Bio production,Gas fermentation,Wood-Ljungdahl pathway,Extracellular electron transport,Redox mediator,Acetogen,Rnf complex,MICROBIAL ELECTROSYNTHESIS,COMMODITY CHEMICALS,CARBON-DIOXIDE,FUELS,ELECTRICITY,FERMENTATION,IMPROVEMENT,ACETOGEN,ETHANOL,SYNGAS},
  language     = {eng},
  pages        = {12},
  title        = {Redox dependent metabolic shift in Clostridium autoethanogenum by extracellular electron supply},
  url          = {http://dx.doi.org/10.1186/s13068-016-0663-2},
  volume       = {9},
  year         = {2016},
}

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