Could Methane Making Microoganisms Solve the C0₂ Problem?

A team of Standford scientists and engineers have solved the mystery behind methanogens, microorganisms which transform electricity and carbon dioxide into methane.

Methanogens are single-celled organisms resembling bacteria. In the team`s study, they demonstrate how methanogens obtain electrons from solid surfaces.

In experiments, the team used a specific species of methanogen named Methanococcus maripaludis. Cultures of M. maripaludis were grown in flasks equipped with a graphite electrode, providing a steady supply of electrons while being fed C0₂.

The methanogens clearly metabolized the C0₂ and a build-up of hydrogen was recorded.

The team wondered if the hydrogen shuttled electrons to the methanogens and to find out, genetically engineered a new strain of M. maripaludis. This new strain had six genes deleted from its DNA, preventing it from producing hydrogenase, which microbes need to make hydrogen.

The mutants were grown in the same conditions as normal methanogens and produced significantly less methane, confirming that hydrogenase and other enzymes take up electrons directly from the electrode surface. This finding contradicts scientists’ assumptions that the microbial cell itself was involved in the transfer.

With these findings, researchers plan to develop large bioreactors where billions of methanogens will crank out methane around the clock.

How Farming Methanogens means Zero Net Emissions

The entire process would be carbon neutral, explains Stanford professor of chemical engineering Alfred Spormann, co-author of the report.

“When microbial methane is burnt as fuel, C0₂ gets recycled back into the atmosphere where it originated,” says Spormann. “Natural gas combustion, on the other hand, frees carbon that has been trapped underground for millions of years.”

The overall goal was to create large bioreactors where microbes convert atmospheric C0₂ and clean electricity from solar, wind or nuclear power into renewable fuels. “Now that we understand how methanogens take up electricity, we can re-engineer conventional electrodes to deliver more electrons to more microbes at a faster rate.”

Methane gas is much more dangerous to the environment than C0₂, but when methane is burnt as a fuel, it generates C0₂, which can be consumed by the methanogens. This means zero net emissions and maybe even a self-renewing fuel source.

However, producing microbial methane on an industrial scale will require major improvements in efficiency, says Stanford postdoctoral scholar Jörg Deutzmann, lead author of the study.

“Right now, the main bottleneck in this process is figuring out how to get more electrons from the electrode into the microbial cell,” says Deutzmann. “To do that, you first have to know how electron uptake works in methanogens. Then you can engineer and enhance the electron-transfer rate and increase methane production.”

At this point, differing theories and evidence provide obstacles to the Stanford team’s end-goal of creating large bioreactors for the methanogens.

"The leading hypothesis is that many microbes, including methanogens, take up electrons directly from the electrode," Deutzmann says. "But in a previous study, we found evidence that microbial enzymes and other molecules could also play a role. From an engineering perspective, it makes a difference if you have to design an electrode to accommodate large microbial cells versus enzymes. You can attach a lot more enzymes to the electrode, because enzymes are a lot smaller."

The study also offers new insights on microbially-influenced corrosion, a biological process that threatens the long-term stability of structures made of iron and steel. "Biocorrosion is a significant global problem," Spormann says. "The yearly economic loss caused by this process is estimated to be in the $1 billion range."