Abstract
In bioelectrochemical systems, the electrode potential is an important parameter affecting the electron flow between electrodes and microbes and microbial metabolic activities. Here, we investigated the metabolic characteristics of a glucose-utilizing strain of engineered Shewanella oneidensis under electrode-respiring conditions in electrochemical reactors for gaining insight into how metabolic pathways in electrochemically active bacteria are affected by the electrode potential. When an electrochemical reactor was operated with its working electrode poised at +0.4 V (vs. an Ag/AgCl reference electrode), the engineered S. oneidensis strain, carrying a plasmid encoding a sugar permease and glucose kinase of Escherichia coli, generated current by oxidizing glucose to acetate and produced D-lactate as an intermediate metabolite. However, D-lactate accumulation was not observed when the engineered strain was grown with a working electrode poised at 0 V. We also found that transcription of genes involved in pyruvate and D-lactate metabolisms was upregulated at a high electrode potential compared with their transcription at a low electrode potential. These results suggest that the carbon catabolic pathway of S. oneidensis can be modified by controlling the potential of a working electrode in an electrochemical bioreactor.
Highlights
The environmental redox state is an important factor determining the growth and metabolic activities of microorganisms because it affects the availability of electron acceptors and cellular energy conservation processes, such as respiration and fermentation [1]
MR-1 has a complete set of genes encoding the phosphoenolpyruvate (PEP):sugar phosphotransferase system for glucose (PTSGlc; ptsHI-crr and ptsG), it is known that this system does not support the growth of bacteria on glucose through the ED and PP pathways
The results of the present study indicate that shifts in the electrode potential and concomitant changes in electric current in bioelectrochemical systems (BES) affect the glycolytic flux towards D-lactate production in the engineered glucose-utilizing MR-1
Summary
The environmental redox state is an important factor determining the growth and metabolic activities of microorganisms because it affects the availability of electron acceptors and cellular energy conservation processes, such as respiration and fermentation [1]. The difference in redox potentials between electron donors and acceptors determines the amount of energy conserved during electron transfer reactions. The intracellular redox balance, which influences fermentative products, is associated with the environmental redox state [2]. The amount of electron acceptors (e.g., oxygen) is used for controlling the production rate and target compound yields [3]. Recent studies have suggested that bioelectrochemical systems (BES) are useful for controlling microbial metabolic activities [4]. BES are biotechnological systems that utilize the PLOS ONE | DOI:10.1371/journal.pone.0138813. BES are biotechnological systems that utilize the PLOS ONE | DOI:10.1371/journal.pone.0138813 September 22, 2015
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