Natural gas has seen a resurgence due to hydraulic fracturing ("fracking") which has allowed geologists and engineers to extract it from wells that were previously considered unusable. CO2 emissions from energy have plummeted back to early 1990s levels and emissions from dirtier forms of energy like coal are back at early 1980s levels.

But transporting natural gas from wellheads to market provides multiple opportunities for its primary constituent, methane, to leak into the atmosphere. It dissipates very quickly compared to CO2 and so only the most aggressive environmental claims try to implicate it in climate change, but it is still waste, which drives up energy cost for the poor. To try and optimize that, an international team of researchers is attempting to convert methane directly to electricity using bacteria, which could be done near the drilling sites. It wouldn't eliminate leakage entirely, but cutting it in half is a win for everyone.

It's still only proof-of-concept, but they have been able to create a bacteria-powered fuel cell that can convert the methane into small amounts of electricity. Basic research in this area would certainly be a better use of the public's money than throwing more subsidies at solar panel corporations.

Microbial fuel cells convert chemical energy to electrical energy using microorganisms. They can run on most organic material, including wastewater, acetate and brewing waste. Methane, however, causes some problems for microbial fuel cells because, while there are bacteria that consume methane, they live in the depths of the ocean and are not currently culturable in the laboratory.

Transmission electron microscopy image of their engineered M. acetivorans strain capturing methane. Credit: Thomas Wood, Penn State

"We know of a bacterium that can produce an energy enzyme that grabs methane," said Thomas K. Wood,professor of chemical engineering at Penn State. "We can't grow them in captivity, but we looked at the DNA and found something from the bottom of the Black Sea and synthesized it."

Funded by U.S. Department of Energy's Advanced Research Projects Agency -- Energy, the researchers actually created a consortium of bacteria that produces electricity because each bacterium does its portion of the job. Using synthetic biological approaches, including DNA cloning, the researchers created a bacterium like those in the depths of the Black Sea, but one they can grow in the laboratory. This bacterium uses methane and produces acetate, electrons and the energy enzyme that grabs electrons. The researchers also added a mixture of bacteria found in sludge from an anaerobic digester -- the last step in waste treatment. This sludge contains bacteria that produce compounds that can transport electrons to an electrode, but these bacteria needed to be acclimated to methane to survive in the fuel cell. 

"We need electron shuttles in this process," said Wood. "Bacteria in sludge act as those shuttles."

Once electrons reach an electrode, the flow of electrons produces electricity. To increase the amount of electricity produced, the researchers used a naturally occurring bacterial genus -- Geobacter, which consumes the acetate created by the synthetic bacteria that captures methane to produce electrons.

To show that an electron shuttle was necessary, the researchers ran the fuel cell with only the synthetic bacteria and Geobacter. The fuel cell produced no electricity. They added humic acids -- a non-living electron shuttle -- and the fuel cells worked. Bacteria from the sludge are better shuttles than humic acids because they are self-sustaining. The researchers have filed provisional patents on this process.

"This process makes a lot of electricity for a microbial fuel cell," said Wood. "However, at this point that amount is 1,000 times less than the electricity produced by a methanol fuel cell."