Potential of Zymomonas mobilis as an electricity producer in ethanol production

Abstract

Background: Microbial fuel cell (MFC) convokes microorganism to convert biomass into electricity. However, most well-known electrogenic strains can not directly use glucose to produce valuable products. Zymomonas mobilis, a promising bacterium for ethanol production, owns special Entner-Doudoroff pathway with less ATP and biomass produced and the low energy-coupling respiration, making Z. mobilis a potential exoelectrogen. Results: A glucose-consumed MFC is constructed by inoculating Z. mobilis. The electricity with power density 2.0 mW m-2 is derived from the difference of oxidation-reduction potential (ORP) between anode and cathode chambers. Besides, two-type electricity generation is observed as glucose-independent process and glucose-dependent process. For the sake of enhancing MFC efficiency, extracellular and intracellular strategies are implemented. Biofilm removal and addition of c-type cytochrome benefits electricity performance and Tween 80 accelerates the electricity generation. Perturbation of cellular redox balance compromises the electricity output, indicating that redox homeostasis is the principal requirement to reach ideal voltage. Conclusion: This study identifies potential feature of electricity activity for Z. mobilis and provides multiple strategies to enhance the electricity output. Therefore, additional electricity generation will benefit the techno-economic viability of the commercial bulk production for biochemicals or biofuels in an efficient and environmentally sustainable manner.

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

“…On the other hand, for most non-electroactive organisms, due to the lack of electron transfer pathway, they are not able to directly deliver or uptake electrons, which severely limited their applications in anodic electro-fermentation or cathodic electro-fermentation. Although addition of redox mediators or surfactants could promote indirect EET and regenerate intracellular reduce equivalents [ 46 , 65 ], their inhibition on the cell growth would be hazard for practical applications. Lastly, to achieve efficient coupling of inward electrons with cell growth and metabolic pathways is a bottleneck in the development of EF.…”

“…Geng et al recently introduced Tween 80 into a Zymomonas mobilis -inoculated bioelectrochemical system and accelerated the electricity generation and ethanol production simultaneously. Tween 80 was used as a surfactant to enhance the permeability cell membranes and transport of various electron shuttles across cell membranes [ 46 ].…”

Electrochemical Control of Cell Metabolism Improves Ethanol Production of Zymomonas mobilis in an Electro-Fermentation System

“…mobilis is supposed to be a suitable candidate for the microbial cell factory because of its remarkable ethanol productivity and potential electro-activity. 10,11 It metabolizes sugar through the Entner−Doudoroff (ED) pathway with less ATP generated for less biomass accumulation. Because ATP is dissipated predominantly during growth for intracellular energy homeostasis, more sugar diverted to the ethanol production pathway achieves a superior ethanol yield and productivity.…”

“…13−15 Interestingly, Z. mobilis has recently been identified as a potential electroactive bacterium due to the incomplete electron-transfer chain in the membrane, which comprises an active branched respiratory chain with type II NADH (nicotinamide adenine dinucleotide) dehydrogenase, coenzyme Q10, cytochrome bd, several c-type cytochrome terminal oxidases, and some minor or still unidentified constituents. 11 Geng et al first reported that Z. mobilis performed electrical activity and generated electricity along with ethanol production when using glucose as the primary substrate. 11 The output of electrons from Z. mobilis might imply the feasibility of using extra electrons from electrodes to regulate the cell metabolic flux in EFS.…”

Genetics and metabolic engineering of yeast strains for efficient ethanol production

“…For this reason, most of the energy is expended on ethanol production rather than cell biomass thereby producing a 2.5‐fold higher substrate conversion rate than S. cerevisiae (Kang & Lee, 2015; Qiu et al, 2020; Willey, Sherwood, & Woolverton, 2017). However, S. cerevisiae is a preferred choice for industrial fermentation due to its reduced purification cost as the low pH of yeast fermentation provides higher sterility of the process which is disadvantaged to Z. mobilis (Fuchino et al, 2020; Geng et al, 2020). Clostridium sp.…”