Radioactive fingerprinting of microorganisms that oxidize atmospheric methane in different soils

Microorganisms that oxidize atmospheric methane in soils were characterized by radioactive labelling with (CH4)-C-14 followed by analysis of radiolabe lled phospholipid ester linked fatty acids (C-14-PLFAs); The radioactive fi ngerprinting technique was used to compare active methanotrophs in soil sam ples from Greenland, Denmark, the United States, and Brazil. The C-14-PLFA fingerprints indicated that closely related methanotrophic bacteria were re sponsible for the oxidation of atmospheric methane in the soils. Significan t amounts of labelled PLFAs produced by the unknown soil methanotrophs coel uted. with a group of fatty acids that included i17:0, a17:0, and 17:1 omeg a 8c (up to 9.0% of the total C-14-PLFAs), These PLFAs are not known to be significant constituents of methanotrophic bacteria. The major PLFAs of the soil methanotrophs (73.5 to 89.0% of the total PLFAs) coeluted with 18:1 a nd 18:0 fatty acids (e.g., 8:1 omega 9, 18:1 omega 7, and 18:0), The C-14-P LFAs fingerprints of the soil methanotrophs that oxidized atmospheric metha ne did not change after long-term methane enrichment at 170 ppm CH4. The C- 14-PLFA fingerprints of the soil methanotrophs were different from the PLFA profiles of type I and type II methanotrophic bacteria described previousl y. Some similarity at the PLFA level was observed between the unknown soil methanotrophs and the PLFA phenotype of the type II methanotrophs, Methanot rophs in Arctic, temperate, and tropical regions assimilated between 20 and 54% of the atmospheric methane that was metabolized. The lowest relative a ssimilation (percent) was observed for methanotrophs in agricultural soil, whereas the highest assimilation was observed for methanotrophs in rain for est soil, The results suggest that methanotrophs with relatively high carbo n conversion efficiencies and very similar PLFA compositions dominate atmos pheric methane metabolism in different soils. The characteristics of the me thane metabolism and the C-14-PLFA fingerprints excluded any significant ro le of autotrophic ammonia oxidizers in the metabolism of atmospheric methan e.