methane emission
A reduction in global burned area in the 2000s had an unexpectedly large impact on methane emissions. NASA/GSFC/SVS

Researchers have identified a long-neglected enzyme which results in the production of methane (CH4), a greenhouse gas produced by organisms through natural processes.

Researchers of University of Washington School of Medicine have detected the role of iron-only nitrogenase enzyme in generating methane. Scientists found that the roughly 10 percent of nitrogen-fixing microorganisms contains genetic code for generation of the enzyme.

The enzyme was earlier known for the production of ammonia from nitrogen gas in microorganisms. The recent research has found that it is also responsible for the production of methane from carbon dioxide. The enzymes produced methane as a sideline by-product while ammonia remained the major product.

Caroline Harwood, a senior author and the Gerald and Lyn Grinstein Professor of Microbiology at the University of Washington School of Medicine said, "Methane is a potent greenhouse gas. That is why it is important to account for all its sources."

A report published in journal Nature Microbiology states that methane released by fossil fuels and microbial activities accounts for about one billion tonnes per year. It is generally consumed by other microorganisms or forms a major share of greenhouse gases in Earth's upper atmosphere.

In another research, it was found that burning fossil fuels contributed to 17 teragrams (1teragram = 110,000 ton) of methane emission while wetlands or rice farming attributed to around 12 telegrams of the gas production. Earth's atmosphere accumulates around 25 teragrams of methane per year. However, methane emission from fires has decreased by four teragrams per year.

Single cell archea, commonly found in harsh environments, are the major methane generators. Scientists have detected complex chemical pathways in these organisms for metabolic activities to result in methane being synthesized.

Methane generation by microorganism has medical significance as they play a vital role in the interaction between microbial communities which inhabit humans and animals. Methane in the gut may result in digestion disorders in animals.

Yanning Zheng, the lead author of the study and a postdoctoral student in Microbiology in University of Washington School of Medicine said, "There is now recent evidence that iron-only nitrogenase is active in microbes more often and in more conditions than we had previously thought."

Researchers conducted tests on four nitrogen-fixing bacterial species having iron-only nitrogenase and found all of them to follow the same behavior. Researchers found that methane emitted by Rhodopseudomonas palustris and other microbes produced a tiny amount of methane which enabled methane-utilizing bacteria to grow in the same culture lab.

Researchers believe that similar microbial community interactions are present in marine sediments, soil and in microbiomes living in humans and animals. Microbes in guts of cattle result in the production of huge quantities of methane globally.