Prof IDs Methane-Munching Bacterium's Environmental Quirks

Researchers at the University of Kansas have identified why certain conditions are required for microorganisms to gobble up methane, the second most significant greenhouse gas.

In a study appearing in the July 17 issue of PNAS, the Journal of the National Academy of Sciences, the KU team shows that the chemical state of copper in the vicinity of methanotrophs – methane-oxidizing bacteria – determines how well these organisms can neutralize methane.

The findings will help other researchers better predict atmospheric methane levels, which affect climate change and global warming.

“It provides an explanation for why we have not been able to predict the rate at which methane is oxidized in soils and wetlands, which is nature's main counterbalance for destroying natural and excess anthropogenic methane production,” said David Graham, KU professor of civil, environmental and architectural engineering and one of the study’s authors.

Graham, who is currently on leave at Newcastle University in the United Kingdom, said methane is the second most consequential greenhouse gas behind carbon dioxide.

The KU study involved Charles Knapp, environmental engineering post-doctoral researcher; David Fowle, assistant professor of geology; Jennifer Roberts, assistant professor of geology; Ezra Kulczycki, geology graduate student; and Graham.

These researchers found certain chemical states of copper are required to allow methane monooxygenase, the enzyme that destroys the methane, to be most active in the bacteria. Enzymes are proteins that accelerate the rate of chemical reactions. This particular enzyme is nature’s most efficient biological mechanism for breaking down methane, a very stable molecule.

In the past, researchers had difficulty determining why there was variability in the capacity of bacteria to consume methane when other conditions appeared right. The KU research team asserted local copper composition in the soil and the presence of the methanobactin molecule might explain the inconsistent methane oxidation patterns in nature.

Copper is a toxic metal to almost all organisms. The methanobactin molecule mediates the selective acquisition of copper from many soils and also protects these key bacteria from the toxic effects of copper.

Now that this chemical relationship is better understood, researchers may be able to calculate the size of the methane-eating methanotroph’s feast based on soil geochemistry.