title: Redox dependent metabolic shift inClostridium autoethanogenumby extracellular electron supply.
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,Clostridiumautoethanogenum. 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 (~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.
authors.affiliation: Centre for Microbial Electrochemical Systems, The University of Queensland, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre, The University of Queensland, Brisbane, QLD 4072 Australia.
authors.forename: Frauke
authors.initials: F
authors.lastname: Kracke
authors.affiliation: Centre for Microbial Electrochemical Systems, The University of Queensland, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre, The University of Queensland, Brisbane, QLD 4072 Australia.
authors.forename: Bernardino
authors.initials: B
authors.lastname: Virdis
authors.affiliation: School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072 Australia.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Bernhardt
authors.affiliation: Centre for Microbial Electrochemical Systems, The University of Queensland, Brisbane, QLD 4072 Australia ; Laboratory of Microbial Ecology and Technology, Faculty of Bioscience Engineering, Universiteit Ghent, Ghent, Belgium.
authors.forename: Korneel
authors.initials: K
authors.lastname: Rabaey
authors.affiliation: Centre for Microbial Electrochemical Systems, The University of Queensland, Brisbane, QLD 4072 Australia ; Advanced Water Management Centre, The University of Queensland, Brisbane, QLD 4072 Australia.
authors.forename: Jens O
authors.initials: JO
authors.lastname: Krömer
keywords: Acetogen; Bio production; Extracellular electron transport; Gas fermentation; Microbial electrosynthesis; Redox mediator; Rnf complex; Wood-Ljungdahl pathway