Researchers at Radboud University, the Netherlands, and the Max Planck Institute for Marine Microbiology, in Germany, have discovered a microorganism that couples the reduction of iron to methane oxidation and could thus be relevant in controlling greenhouse gas emissions.

The team of microbiologists and biogeochemists discovered an archaeon—the other branch of ancient prokaryotes besides bacteria—of the order Methanosarcinales that uses iron to convert methane into carbon dioxide. During that process, reduced iron becomes available to other bacteria. Consequently, the microorganism initiates an energy cascade influencing the iron and methane cycle and thus methane emissions.

The discovery could hold significance for rice paddies, which account for 20% of human-related methane emissions. Image credit: Pixabay.The discovery could hold significance for rice paddies, which account for 20% of human-related methane emissions. Image credit: Pixabay. Moreover, these archaea also can also turn nitrate into ammonium—the favorite food of anammox bacteria, which turn ammonium into nitrogen gas without using oxygen.

“This is relevant for wastewater treatment," says Boran Kartal, a microbiologist who recently moved from Radboud University to the Max Planck Institute. “A bioreactor containing anaerobic methane and ammonium-oxidizing microorganisms can be used to simultaneously convert ammonium, methane and oxidized nitrogen in wastewater into harmless nitrogen gas and carbon dioxide, which has much lower global warming potential.”

The same process could also be important in paddy fields, for example, which account for around 20% of human-related emissions of methane.

While there have been numerous indications that such iron-dependent methane oxidizers existed, researchers have never been able to isolate them. Oddly, the Radboud University researchers "discovered" them in enrichment cultures that they had had in their lab for years.

After obtaining a large amount of biomass by feeding them with methane and nitrate, the researchers hypothesized—based on the genetic blueprint of the microorganisms—that they could also convert particulate iron coupled to methane oxidation. Testing in the lab proved that hypothesis correct.

In the next step, Kartal wants to look more closely into the details of the process. “These findings fill one of the remaining gaps in our understanding of anaerobic methane oxidation. Now we want to further investigate which protein complexes are involved in the process,” he says.

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