Insights into catalysts of environmental methane oxidation across landscapes

Aerobic methane oxidation has evolved in the biosphere multiple times. Studies of aerobic methanotrophy have focused on two proteins: soluble methane monooxygenase (sMMO) and particulate methane monooxygenase (pMMO). Laboratory experiments and field observations, however, indicate that these are not the only proteins capable of oxidizing methane and other small hydrocarbons in the environment, even at low substrate concentrations. We have measured methane gas fluxes in a variety of landscapes, including rivers, floodplains, permafrost, desert, oak woodland, and arid rangeland, over a multiyear series of field expeditions in Alaska and California. These environments include a wide range of temperature (subzero to > 40 ºC), moisture, and methane concentration conditions. We observe substantial Alaska riverine methane concentrations, in some cases surpassing deep sea methane concentrations near methane seeps. Across these varied landscapes and conditions, we observe significant soil methanotrophy. Using environmental sampling, amplicon-based soil and water microbial community composition, metagenomic analyses, and bioinorganic chemistry, we provide new insights into an expanded range of metalloproteins that may be able to accomplish methane oxidation across a wide variety of environments.