The Role of Copper Ions in Regulating Methane Monooxygenases in Methanotrophs

Abstract

Methanotrophs are a unique group of Gram-negative methane-oxidizing bacteria that grow aerobically on methane as their sole carbon and energy source (1). Some methanotrophs can also be grown on methanol; however, they are generally considered to be obligate in their requirement for one-carbon compounds and cannot be grown on other multicarbon substrates. Since 1970, they have received considerable attention from microbiologists and industrialists because they can be exploited in biotransformations and bioremediation processes (2). For example, they can be used to convert propylene to propylene oxide and they can degrade the groundwater pollutant trichloroethylene. They are also used in the production of single-cell protein from methane, a relatively inexpensive feedstock. In addition to their commercial potential, methanotrophs also play a key role in the cycling of methane in the natural environment because they oxidize much of the methane produced in anaerobic sediments such as wetlands, peat bogs, and paddy fields, thereby mitigating release of methane to the atmosphere and reducing global warming. It is also now clear that some methanotrophs in aerobic soils can oxidize atmospheric concentrations of methane (e.g., 1–2 ppm), thereby further reducing global warming as a result of methane. Methane-oxidizing bacteria can be enriched for and isolated from a wide variety of environments, including freshwater, sediments, soils, seawater, peat bogs, tundra, paddy fields, and hot springs.