Wetlands are a major source of atmospheric methane (Image: Olli Malmivaara/Getty)

From cow burps to tree hiccups and melting permafrost, the potent greenhouse gas methane is produced in myriad ways. Now we can add another one to the list: electricity-generating microbes. The finding could one day allow us to control the generation of methane.

Methanosaeta microbes are one of the biggest natural producers of methane. They live in waste water and wetlands and were thought to break down acetate supplied by other nearby microbes, releasing methane and carbon dioxide in the process.

One of the neighbours of these Methanosaeta microbes, Geobacter bacteria, have a talent of their own. These bacteria shuttle electrons between one another using threadlike projections called pili.


Because species of these two genuses often colonise the same habitats, Amelia-Elena Rotaru at the University of Massachusetts, Amherst, wondered whether the Geobacter species might also be providing electrons to the Methanosaeta.

To find out, her team cultured strains of both together. They found that methane production stopped when the Geobacter species was genetically engineered to prevent it from producing the conducting pili.

Carbon diet

This suggests that Methanosaeta microbes are taking electrons from the Geobacter species. To see what they do with them the team exposed the cultured strains to a source of carbon dioxide in which the carbon atoms were swapped with a different carbon isotope. This enabled the team to track the carbon atoms as they were shuttled from carbon dioxide to the newly formed methane.

Because the Methanosaeta microbes have genes that allow them to reduce carbon dioxide, together the results suggest that the microbes are using the electrons to reduce the carbon dioxide in the atmosphere to methane, via a process known as direct interspecies electron transfer (DIET).

This doesn’t rule out the acetate generation, but it suggests that DIET is the dominant process in waste water.

If the finding can be replicated in water from wetlands, the largest source of naturally generated methane, it might mean that electron transfer could well be the largest mode of natural methane generation, says Rotaru.

She says the new finding could give us the power to control the generation of this source of methane at the flick of a switch. Interrupt the electrical connection between the microbes to turn off production in wetlands where it contributes to global warming; re-establish it whenever we wish to convert waste biomass to natural gas.

Once the process is better studied, she adds, climate models built assuming other modes of methane generation may have to be re-evaluated.

Journal reference: Energy and Environmental Science, DOI: 10.1039/C3EE42189A