The research, published Monday in the journal Nature Communications, could help rice farmers limit the effects of the world's most popular grain on the climate.
Rice cultivation accounts for 5 percent of global methane emissions. Though less abundant than CO2, the greenhouse gas effect of methane is 25 times more than of carbon dioxide.
When rice fields are flooded, the soil becomes depleted of oxygen, producing an environment in which methane-producing microorganisms thrive.
Scientists in Denmark theorized that cable bacteria, filamentous bacteria that can conduct electricity across short distances, could make life in flooded rice fields less friendly to methane-emitting microbes. To test their theory, researchers grew rice with and without cable bacteria applications in the lab.
"The difference was far beyond my expectations," Vincent Valentin Scholz, who conducted the experiments while working as a doctoral student at Aarhus University's Center for Electromicrobiology, said in a news release. "The pots with cable bacteria emitted 93 percent less methane than the pots without cable bacteria."
Like methane-emitting microbes, cable bacteria also thrive in oxygen-deprived environs. The bacteria are often found at the bottoms of oceans, lakes and rivers. The bacteria form in chains of thousands of cells. The outer layer of the chain uses the difference in oxygen levels in the water and sediment to drive an electrical current. The flow of electricity helps the bacteria metabolize energy.
"Cable bacteria transport electrons over centimeter distances along their filaments, changing the geochemical conditions of the water-saturated soil," Vincent Valentin Scholz said. "The cable bacteria recycle the soil's sulfur compounds, thus maintaining a large amount of sulfate in the soil. This has the consequence that the methane-producing microbes cannot maintain their activity."
Previous studies have shown scattering sulfate on rice fields slows methane emissions, but the benefit is temporary. The latest research suggests the addition of cable bacteria can provide a more long-term solution.
Scientists plan to conduct field experiments to ensure the promising results of the lab tests can be replicated in actual rice paddies.
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