Biological oxidation of CH(4) is an important constraint on the emission of this gas from areas, such as landfills to the atmosphere. We studied the effect of temperature on methanotrophic bacteria in three different landfill cover soils, incubated in the laboratory. In samples of a young cover, consisting of wood chips and sewage sludge, the phospholipid fatty acids (PLFAs), regarded as biomarkers for type I methanotrophs (16:1omega5t, 16:1omega6c, 16:1omega8c), primarily increased at low temperatures (5-10 degrees C). On the other hand, the PLFA marker for type II methanotrophs (18:1omega8c) was highly elevated only at 20 degrees C. These results suggest that temperature can determine the selection of methanotroph populations.