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Development of bioelectrocatalytic activity stimulates mixed-culture reduction of glycerol in a bioelectrochemical system.

ABSTRACT: In a microbial bioelectrochemical system (BES), organic substrate such as glycerol can be reductively converted to 1,3-propanediol (1,3-PDO) by a mixed population biofilm growing on the cathode. Here, we show that 1,3-PDO yields positively correlated to the electrons supplied, increasing from 0.27?±?0.13 to 0.57?±?0.09?mol PDO?mol(-1) glycerol when the cathodic current switched from 1?A?m(-2) to 10?A?m(-2) . Electrochemical measurements with linear sweep voltammetry (LSV) demonstrated that the biofilm was bioelectrocatalytically active and that the cathodic current was greatly enhanced only in the presence of both biofilm and glycerol, with an onset potential of -0.46?V. This indicates that glycerol or its degradation products effectively served as cathodic electron acceptor. During long-term operation (>?150 days), however, the yield decreased gradually to 0.13?±?0.02?mol PDO?mol(-1) glycerol, and the current-product correlation disappeared. The onset potentials for cathodic current decreased to -0.58?V in the LSV tests at this stage, irrespective of the presence or absence of glycerol, with electrons from the cathode almost exclusively used for hydrogen evolution (accounted for 99.9% and 89.5% of the electrons transferred at glycerol and glycerol-free conditions respectively). Community analysis evidenced a decreasing relative abundance of Citrobacter in the biofilm, indicating a community succession leading to cathode independent processes relative to the glycerol. It is thus shown here that in processes where substrate conversion can occur independently of the electrode, electroactive microorganisms can be outcompeted and effectively disconnected from the substrate.

SUBMITTER: Zhou M

PROVIDER: S-EPMC4408180 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Development of bioelectrocatalytic activity stimulates mixed-culture reduction of glycerol in a bioelectrochemical system.

Zhou Mi M Freguia Stefano S Dennis Paul G PG Keller Jürg J Rabaey Korneel K

Microbial biotechnology 20150326 3

In a microbial bioelectrochemical system (BES), organic substrate such as glycerol can be reductively converted to 1,3-propanediol (1,3-PDO) by a mixed population biofilm growing on the cathode. Here, we show that 1,3-PDO yields positively correlated to the electrons supplied, increasing from 0.27 ± 0.13 to 0.57 ± 0.09 mol PDO mol(-1) glycerol when the cathodic current switched from 1 A m(-2) to 10 A m(-2) . Electrochemical measurements with linear sweep voltammetry (LSV) demonstrated that the b ...[more]

PMID: 25817314

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Project description:BackgroundElectro-fermentation (EF) is an emerging tool for bioprocess intensification. Benefits are especially expected for bioprocesses in which the cells are enabled to exchange electrons with electrode surfaces directly. It has also been demonstrated that the use of electrical energy in BES can increase bioprocess performance by indirect secondary effects. In this case, the electricity is used to alter process parameters and indirectly activate desired pathways. In many bioprocesses, oxidation-reduction potential (ORP) is a crucial process parameter. While C. pasteurianum fermentation of glycerol has been shown to be significantly influenced electrochemically, the underlying mechanisms are not clear. To this end, we developed a system for the electrochemical control of ORP in continuous culture to quantitatively study the effects of ORP alteration on C. pasteurianum by metabolic flux analysis (MFA), targeted metabolomics, sensitivity and regulation analysis.ResultsIn the ORP range of -462 mV to -250 mV, the developed algorithm enabled a stable anodic electrochemical control of ORP at desired set-points and a fixed dilution rate of 0.1 h-1. An overall increase of 57% in the molar yield for 1,3-propanediol was observed by an ORP increase from -462 to -250 mV. MFA suggests that C. pasteurianum possesses and uses cellular energy generation mechanisms in addition to substrate-level phosphorylation. The sensitivity analysis showed that ORP exerted its strongest impact on the reaction of pyruvate-ferredoxin-oxidoreductase. The regulation analysis revealed that this influence is mainly of a direct nature. Hence, the observed metabolic shifts are primarily caused by direct inhibition of the enzyme upon electrochemical production of oxygen. A similar effect was observed for the enzyme pyruvate-formate-lyase at elevated ORP levels.ConclusionsThe results show that electrochemical ORP alteration is a suitable tool to steer the metabolism of C. pasteurianum and increase product yield for 1,3-propanediol in continuous culture. The approach might also be useful for application with further anaerobic or anoxic bioprocesses. However, to maximize the technique's efficiency, it is essential to understand the chemistry behind the ORP change and how the microbial system responds to it by transmitted or direct effects.

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Development of bioelectrocatalytic activity stimulates mixed-culture reduction of glycerol in a bioelectrochemical system.

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Development of bioelectrocatalytic activity stimulates mixed-culture reduction of glycerol in a bioelectrochemical system.

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