Characterization of methanotrophic bacterial populations in soils showing atmospheric methane uptake

The global methane cycle includes both terrestrial and atmospheric processe s and may contribute to feedback regulation of the climate. Most oxic soils are a net sink for methane, and these soils consume approximately 20 to 60 Tg of methane per year. The soil sink for atmospheric methane is microbial ly mediated and sensitive to disturbance. A decrease in the capacity of thi s sink may have contributed to the similar to 1%.year(-1) increase in the a tmospheric methane level in this century. The organisms responsible for met hane uptake by soils (the atmospheric methane sink) are not known, and fact ors that influence the activity of these organisms are poorly understood. I n this study the soil methane-oxidizing population was characterized by bot h labelling soil microbiota with (CH4)-C-14 and analyzing a total soil mono oxygenase gene library. Comparative analyses of [C-14]phospholipid ester-li nked fatty acid profiles performed with representative methane-oxidizing ba cteria revealed that the soil sink for atmospheric methane consists of an u nknown group of methanotrophic bacteria that exhibit some similarity to typ e II methanotrophs. An analysis of monooxygenase gene libraries from the sa me soil samples indicated that an unknown group of bacteria belonging to th e ct subclass of the class Proteobacteria was present; these organisms were only distantly related to extant methane-oxidizing strains. Studies on fac tors that affect the activity, population dynamics, and contribution to glo bal methane flux of "atmospheric methane oxidizers" should be greatly facil itated by use of biomarkers identified in this study.