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Bacteria turn methane into electricity

By F. Pelayo García de Arquer August 9, 2017
microbial-fuel-cell
Schematic of a microbial fuel cell capable of producing electricity from methane at high Coulombic efficiency. Credit: Nature Communications

Researchers from The Pennsylvania State University (Penn State) have demonstrated a system capable of directly converting methane into electricity using microbial fuel cells. A microbial fuel cell is a system that transforms a fuel into electricity and vice versa using microbes. Microbial systems capable of generating methane from electricity and CO2, a process known as methanogenesis, have been previously reported. However, the successful demonstration of the inverse process—one that would produce electrons and CO2 from methane—had remained thus far elusive. The work, led by Thomas K. Wood, has been published in Nature Communications.

As reported in the article, Michael J. McAnulty from Penn State and colleagues have built a bacteria consortium—that is, microbial groups living symbiotically—that first converts methane to acetate and then converts this acetate to electrons at high Coulombic efficiency—a measure of how efficiently electrons are being generated from a methane molecule—generating a significant electrical current. Wood says, “This is the first time methane has been converted to electricity by bacteria (previous reports have values too low to be considered successful). Also, this work confirms that we have reversed methanogenesis by engineering an archaeal strain to produce an enzyme that captures methane (methane reductase).” Wood states that they had evidence that this could be doable from prior works, where they had engineered a similar bacterial strain to be compatible with methane, and observed electron interactions. According to Wood, “The most challenging problem was getting the correct consortium of organisms to provide sufficient electron carriers; this was solved by adding the bacteria of a methane-acclimated sludge.”

Thomas Mallouk from Penn State, who was not involved with this study, explains the importance of reducing methane emissions: “Methane is a very potent greenhouse gas, with something like 80 times the warming potential of an equivalent amount of CO2. Fugitive methane from pipeline leaks can be a significant contributor to climate change.” He acknowledges that Wood’s approach is “definitely a clever solution to a tricky chemical problem, i.e., how to extract electrical energy efficiently from methane.”

Wood says their strategy can be improved even further, “Current limitations are electron transfer to the anode and capturing the methane by the engineered archaeal strain (via the methane reductase). Rates are about as good as any microbial fuel cell (but should be improved).” Pushing the rate of their microbial fuel cells to that of conventional, more developed standard fuel cells will open the door to the deployment of such microbial approach. Geoffrey Ozin, from University of Toronto and not involved in this study, says that further advances may come by simultaneously solving the excessive methane emissions and those of its combustion companion, CO2. Such a system would be transformative toward battling climate change.

Read the article in Nature Communications.