Enhanced electron transfer of different mediators for strictly opposite shifting of metabolism in Clostridium pasteurianum grown on glycerol in a new electrochemical bioreactor

Abstract

Microbial electrosynthesis or electro-fermentation in bioelectrochemical systems (BES) have recently received much attention. Here, we demonstrate with the glycerol metabolism by Clostridium pasteurianum that H 2 from in situ water electrolysis, especially in combination with a redox mediator, provides a simple and flexible way for shifting product selectivity and enhancing product yield in the fermentation process. In particular, we report and quantify for the first time strictly different effects of Neutral Red (NR) and the barely studied redox mediator Brilliant Blue (BB) on the growth and product formation of C. pasteurianum grown on glycerol in a newly developed BES. We were able to switch the product formation pattern of C. pasteurianum with a concentration-dependent addition of NR and BB under varied iron availability.Interestingly, NR and BB influenced the glycerol metabolism in a strictly opposite manner concerning the formation of the major products 1,3-propanediol (1,3-PDO) and n-butanol (BuOH). Whereas, NR and iron generally enhance the formation of BuOH, BB favors the formation of 1,3-PDO. In BES the metabolic shifts were enhanced, leading to a further increased yield by as high as 33% for BuOH in NR fermentations and 21% for 1,3-PDO in BB fermentations compared with the respective controls. For the first time, the electron transfer mediated by these mediators and their recycle (recharge) were unambiguously quantified by excluding the overlapping effect of iron. BB has a higher capacity than NR and iron. The extra electron transfer by BB can account for as high as 30-75% of the total NAD + regeneration under certain conditions, contributing significantly to the product formation.

Microbial electro-fermentation for synthesis of chemicals and biofuels driven by bi-directional extracellular electron transfer

“…(B) 2,3-butanediol production in a hydrogenase-deficient S. oneidensis using native Mtr proteins and exogenous light-driven proton pump (proteorhodopsin) for NADH accumulation [52] . (C) Different effects of neutral red (NR) and the barely studied redox mediator brilliant blue (BB) on the growth and product formation of C. pasteurianum grown on glycerol in a newly developed bioelectrochemical system [54] . (D) Chiral alcohol (R)-1-phenylethanol production from acetophenone in engineered E. coli by using methyl viologen (MV) as mediator to achieve EET [55] .…”

“…Rowe et al found that methyl viologen (MV) shuttled electrons from water-soluble abiotic photosensitizers into S. oneidensis MR-1 to support target reactions including H 2 evolution, CO 2 reduction, succinate and lactate production [ 53 ]. Utesch et al reported a newly developed bioelectrochemical system of C. pasteurianum grown on glycerol by adding artificial mediators neutral red (NR) and brilliant blue (BB) with different electrochemical properties [ 54 ]. The addition of NR leaded to metabolic shifts in BES and increased the n‐butanol yield by as high as 33%, while BB preferred to enhance the formation of 1,3‐propanediol ( Fig.…”

Enhancing Biosynthesis and Manipulating Flux in Whole Cells with Abiotic Catalysis

“…Utesch et al. compared the effects of Brilliant Blue (BB) and NR in both iron‐limiting and iron‐excess conditions on butanol and 1,3‐PDO production during glycerol fermentation with Clostridium pasteurianum [37] . Iron itself was able to act as a mediator under BES conditions.…”

Same but different–Scale up and numbering up in electrobiotechnology and photobiotechnology

“…stirred tank and bubble column). This system has been successfully used for in situ generation of H 2 and O 2 , control of redox potential and recharge of electron mediator for electricity‐aided production of 1,3‐propanediol and n ‐butanolin laboratory scales (0.5 and 2.5 L) . Another design which may be suitable for a rational scale up is an electrochemical bubble column reactor.…”