Engineering Shewanella oneidensis enables xylose-fed microbial fuel cell

Abstract

BackgroundThe microbial fuel cell (MFC) is a green and sustainable technology for electricity energy harvest from biomass, in which exoelectrogens use metabolism and extracellular electron transfer pathways for the conversion of chemical energy into electricity. However, Shewanella oneidensis MR-1, one of the most well-known exoelectrogens, could not use xylose (a key pentose derived from hydrolysis of lignocellulosic biomass) for cell growth and power generation, which limited greatly its practical applications.ResultsHerein, to enable S. oneidensis to directly utilize xylose as the sole carbon source for bioelectricity production in MFCs, we used synthetic biology strategies to successfully construct four genetically engineered S. oneidensis (namely XE, GE, XS, and GS) by assembling one of the xylose transporters (from Candida intermedia and Clostridium acetobutylicum) with one of intracellular xylose metabolic pathways (the isomerase pathway from Escherichia coli and the oxidoreductase pathway from Scheffersomyces stipites), respectively. We found that among these engineered S. oneidensis strains, the strain GS (i.e. harbouring Gxf1 gene encoding the xylose facilitator from C. intermedi, and XYL1, XYL2, and XKS1 genes encoding the xylose oxidoreductase pathway from S. stipites) was able to generate the highest power density, enabling a maximum electricity power density of 2.1 ± 0.1 mW/m2.ConclusionTo the best of our knowledge, this was the first report on the rationally designed Shewanella that could use xylose as the sole carbon source and electron donor to produce electricity. The synthetic biology strategies developed in this study could be further extended to rationally engineer other exoelectrogens for lignocellulosic biomass utilization to generate electricity power.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0881-2) contains supplementary material, which is available to authorized users.

Complete Oxidation of Xylose for Bioelectricity Generation by Reconstructing a Bacterial Xylose Utilization Pathway in vitro

“…Compared to the single‐step oxidation of a xylose‐based EFC, the power density dramatically increased as well as the Faraday efficiency . Indeed, the xylose consumption rate in vitro (≈500 μ m h −1 ) is much higher than that in engineered Shewanella (≈35.2 μ m h −1 ) based on a previous study . Our higher reaction rate in an EFC represents a striking advantage of the in vitro enzymatic pathway over an in vivo biosystem because the latter usually suffers from low volumetric catalytic activity resulting from the dilution effect of cell mass, and a slow mass transfer owing to the cell compartment and the presence of the membrane …”

“…However, owing to the complexity of these natural xylose utilization pathways and the insufficient exploitation of associated oxidoreductases, only a few examples of the use of xylose as a fuel for fuel cells have been reported, based on the bioconversion of the microorganism consortium from wastewater . Recently, an engineered Shewanella oneidensis that incorporated xylose transporters and xylose utilization pathways has been constructed to generate electricity through microbial fuel cells . Xia et al.…”

Modular engineering to increase intracellular NAD(H/+) promotes rate of extracellular electron transfer of Shewanella oneidensis

“…In the last decade, extensive studies on exoelectrogens were conducted from multidisciplinary fields to elucidate fundamental mechanisms of EET. Many approaches to promote power generation primarily involved facilitating EET between bacteria and electrodes to promote the EET rate 20 , 21 , including broadening and strengthening substrate utilization 60 , optimizing conductive c -type cytochromes systems 61 , promoting electron shuttle biosynthesis and transportation 39 , 40 , 62 , and constructing electroactive biofilms 41 . However, whether the intracellular electrons pool had any effect on the EET rate remained uncharacterized.…”

Electroactive microorganisms in bioelectrochemical systems

“…Several genetic engineering studies focused on the model exoelectrogen S. oneidensis to improve its substrate range and overall electron flux. Adding genes that encode metabolic pathways from other microorganisms, including E. coli, Zymomonas mobilis, Candida intermedia and Clostridium acetobutylicum, has expanded the substrate range of different S. oneidensis strains from 2-and 3carbon molecules to 5-and 6-carbon molecules, such as xylose 117 , glucose 118 and glycerol 119 . The addition of a light-driven proton pump from a marine bacterium increased the proton motive force of S. oneidensis and consequently its substrate uptake rate, resulting in a 250% increase in current production 120 .…”