Methane-producing microorganism makes a meal of iron

A new understanding of how a microorganism uses iron to more efficiently conserve energy when producing methane and carbon dioxide will allow researchers to make important predictions of future climate change and maybe even manipulate the production of these greenhouse gasses.
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A new understanding of how an important methane-producing microorganism creates methane and carbon dioxide could eventually allow researchers to manipulate how much of these important greenhouse gases escape into the atmosphere. A new study by Penn State researchers proposes an updated biochemical pathway that explains how the microorganism uses iron to more efficiently capture energy when producing methane. The study appears online in the journal Science Advances.

“The microorganism Methanosarcina acetivorans is a methanogen that plays an important part in the , by which dead plant material is recycled back into  that then generates new plant material by photosynthesis,” said James Ferry, Stanley Person Professor of Biochemistry and Molecular Biology at Penn State, who led the research team. “Methanogens produce about 1 billion metric tons of  annually, which plays a critical role in . Understanding the process by which this microorganism produces methane is important for predicting future climate change and for potentially manipulating how much of this greenhouse gas the organism releases.”

Methanosarcina acetivorans, which is found in environments like the ocean floor and  where it helps to decompose dead plant material, converts  into methane and carbon dioxide. Prior to this study, however, researchers were not certain how the microorganism had enough energy to survive in the oxygen-free—anaerobic—environments where it lives. The researchers determined that an oxidized form of  called “iron three,” essentially rust, allows the microorganism to work more efficiently, using more acetic acid, creating more methane, and creating more ATP—a chemical that provides energy for biological reactions essential for growth.

“Most organisms like humans use a process called respiration to create ATP, but this requires oxygen,” said Ferry. “When no oxygen is present, many organisms instead use a less efficient process called fermentation to create ATP, like the processes used by yeast in the production of wine and beer. But the presence of iron allows M. acetivorans to use respiration even in the absence of oxygen.”

The findings allowed the researchers to update the biological pathway by which M. acetivorans converts acetic acid to methane, which now includes respiration. Pathways like this one involve many intermediate steps, during which energy is often lost in the form of heat. The researchers also determined that in the presence of iron, energy loss in this microorganism is reduced due to a recently discovered process called electron bifurcation.

“Electron bifurcation takes one of those steps that has the potential for tremendous heat loss and harvests that energy in the form of ATP rather than heat,” said Ferry. “This makes the process more efficient.”

This updated pathway could allow researchers to predict the amount of methane that the microorganism will release into the atmosphere.

“Rice paddies—a major source of the methane in the atmosphere—contain decaying rice plants submerged in water that are ultimately processed by M. acetivorans. If we measure the amount of iron three present in the paddies, we can predict how much methane will be released by the , which can improve our climate change models.”

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