Electron carriers increase electricity production in methane microbial fuel cells that reverse methanogenesis

Background: We previously reversed methanogenesis in microbial fuel cells (MFCs) to produce electricity for the first time from methane by combining an engineered archaeal strain that produces methyl-coenzyme M reductase from unculturable anaerobic methanotrophs (to capture methane and secrete acetate) with Geobacter sulfurreducens (to produce electrons from the generated acetate) and methane-acclimated sludge (to provide electron shuttles). Results: Here, the power density in MFCs was increased 77-fold to 5216 mW/m² and the current density in MFCs was increased 73-fold to 7.3 A/m² by reducing the surface area of the cathode (to make reasonable comparisons to other MFCs), by changing the order the strains of the consortium were added to the anode compartment, and by adding additional electron carriers (e.g., humic acids and cytochrome C). Conclusions: This power density and current density are comparable to the best for any MFC, including those with Shewanella and Geobacter spp. that utilize non-gaseous substrates. In addition, we demonstrate the methane MFC may be used to power a fan by storing the energy in a capacitor. Hence, MFCs that convert methane to electricity are limited by electron carriers.