Construction of an Electron Transfer Mediator Pathway for Bioelectrosynthesis by Escherichia coli.

Jiao Feng,Sheng Xu,Pingkai Ouyang,Kequan Chen,Xin Wang,Kang Li,Qiuhao Lu

doi:10.3389/fbioe.2020.590667

Jiao Feng, Sheng Xu + Show 5 more

Open Access

https://doi.org/10.3389/fbioe.2020.590667

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Abstract

Microbial electrosynthesis (MES) or electro-fermentation (EF) is a promising microbial electrochemical technology for the synthesis of valuable chemicals or high-value fuels with aid of microbial cells as catalysts. By introducing electrical energy (current), fermentation environments can be altered or controlled in which the microbial cells are affected. The key role for electrical energy is to supply electrons to microbial metabolism. To realize electricity utility, a process termed inward extracellular electron transfer (EET) is necessary, and its efficiency is crucial to bioelectrochemical systems. The use of electron mediators was one of the main ways to realize electron transfer and improve EET efficiency. To break through some limitation of exogenous electron mediators, we introduced the phenazine-1-carboxylic acid (PCA) pathway from Pseudomonas aeruginosa PAO1 into Escherichia coli. The engineered E. coli facilitated reduction of fumarate by using PCA as endogenous electron mediator driven by electricity. Furthermore, the heterologously expressed PCA pathway in E. coli led to better EET efficiency and a strong metabolic shift to greater production of reduced metabolites, but lower biomass in the system. Then, we found that synthesis of adenosine triphosphate (ATP), as the “energy currency” in metabolism, was also affected. The reduction of menaquinon was demonstrated as one of the key reactions in self-excreted PCA-mediated succinate electrosynthesis. This study demonstrates the feasibility of electron transfer between the electrode and E. coli cells using heterologous self-excreted PCA as an electron transfer mediator in a bioelectrochemical system and lays a foundation for subsequent optimization.

Highlights

Microbial electrosynthesis (MES) or electro-fermentation (EF) relies on microbial cells as catalysts to increase terminal production of high value fuels and chemicals via electricity (Schroder et al, 2015)
Similar to the data presented by our previous reports (Feng et al, 2018), a significant peak of phenazine-1-carboxylic acid (PCA) was found in the extracts of E. coli-phz, while no PCA synthesis was observed in E. coli BA102 (Supplementary Figure 2)
These results reflect that the phzA1-G1 gene from P. aeruginosa PAO1 was efficiently expressed and PCA was synthesized in E. coliphz

Summary

INTRODUCTION

Microbial electrosynthesis (MES) or electro-fermentation (EF) relies on microbial cells as catalysts to increase terminal production of high value fuels and chemicals via electricity (Schroder et al, 2015). The currently reported self-secreted electron mediators are mostly produced and secreted by electrochemically active bacteria (EAB) to facilitate electron transfer from the cathode. In our previous our work, we established that PCA could perform the role of electron transfer and effectively improve current generation in microbial fuel cell by introducing the PCA pathway of P. aeruginosa in E. coli (Feng et al, 2018). The heterologously expressed PCA pathway was employed to transfer electrons from the cathode to the microbial cells and achieve reduction of fumarate in bioelectrochemical reactors at negative cathode potential. We found that adenosine triphosphate (ATP), as the “energy currency,” was stimulated by the electrical current through the cathode provided by the inward EET process utilizing the heterologously self-excreted PCA in E. coli

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT