THE REGULATION OF METHANE OXIDATION IN SOIL

The atmospheric concentration of methane, a greenhouse gas, has more t han doubled during the past 200 years. Consequently, identifying the f actors influencing the flux of methane into the atmosphere is becoming increasingly important. Methanotrophs, microaerophilic organisms wide spread in aerobic soils and sediments, oxidize methane to derive energ y and carbon for biomass. In so doing, they play an important role in mitigating the flux of methane into the atmosphere. Several physico-ch emical factors influence rates of methane oxidation in soil, including soil diffusivity; water potential; and levels of oxygen, methane, amm onium, nitrate, nitrite, and copper. Most of these factors exert their influence through interactions with methane monooxygenase (MMO), the enzyme that catalyzes the reaction converting methane to methanol, the first step in methane oxidation. Although biological factors such as competition and predation undoubtedly play a role in regulating the me thanotroph population in soils, and thereby limit the amount of methan e consumed by methanotrophs, the significance of these factors is unkn own. Obtaining a better understanding of the ecology of methanotrophs will help elucidate the mechanisms that regulate soil methane oxidatio n.