Engineering Electrode-Attached Microbial Consortia for High-Performance Xylose-Fed Microbial Fuel Cell

The microbial fuel cell (MFC) is a promising technology for energy harvesting from biomass; however, previously reported MFCs with wild-type or biologically modified exoelectrogenic bacteria such as Shewanella oneidensis have often exhibited poor performance in generating electricity from sugars. Herein, a synthetic fermenter-exoelectrogen (Escherichia coli-S. oneidensis) microbial consortium was developed to expand the spectrum of carbon sources for MFC through establishing a highly electroactive anodic biofilm by rationally tuning its microbial community profile to favor efficient electron transfer. Specifically, a synthetic riboflavin pathway from Bacillus subtilis was incorporated into E. coli to overproduce flavins to facilitate flavin-mediated electron transfer, and a highly hydrophobic S. oneidensis strain CP2-1-S1 was adopted as the exoelectrogen to increase its adhesion to the carbon electrode. The highly hydrophobic interactions between S. oneidensis and the anode along with the overproduced flavins (increased from 3.3 μM to 115.2 μM) by the recombinant E. coli provided a definite advantage for S. oneidensis over E. coli in the attachment to the anode surface. Compared with the structure of the wild-type community immobilized on the anode, the cell number of S. oneidensis increased by ∼3 times, whereas the cell number of E. coli decreased by 93.3% in the engineered electrode-attached community. Such rationally engineered anodic biofilm with the tuned microbial community profile (the percentage of S. oneidensis cells in the anodic biofilm increased from 48.2% to 98.2%) showed a much higher catalytic current (from 0.19 to 1.84 A/m2 at 0 V vs SHE). The xylose-fed MFC inoculated with our engineered microbial consortium generated a maximum power density of 728.6 mW/m2, which was 6.8 times higher than that inoculated with wild-type coculture (92.8 mW/m2).