Effect of temperature on composition of the methanotrophic community in rice field and forest soil

Temperature change affects methane consumption in soil. However, there is no information on possible temperature control of methanotrophic bacterial populations. Therefore, we studied CH4 consumption and populations of methanotrophs in an upland forest soil and a rice field soil incubated at different temperatures between 5 and 45 degrees C for up to 40 days. Potential methane consumption was measured at 4% CH4. The temporal progress of CH4 consumption indicated growth of methanotrophs. Both soils showed maximum CH4 consumption at 25-35 degrees C, but no activity at > 40 degrees C. In forest soil CH4 was also consumed at 5 degrees C, but in rice soil only at 15 degrees C. Methanotroph populations were assessed by terminal restriction fragment length polymorphism (T-RFLP) targeting particulate methane monooxygenase (pmoA) genes. Eight T-RFs with relative abundance > 1% were retrieved from both forest and rice soil. The individual T-RFs were tentatively assigned to different methanotrophic populations (e.g. Methylococcus/Methylocaldum, Methylomicrobium, Methylobacter, Methylocystis/Methylosinus) according to published sequence data. Two T-RFs were assigned to ammonium monooxygenase (amoA) gene sequences. Statistical tests showed that temperature affected the relative abundance of most T-RFs. Furthermore, the relative abundance of individual T-RFs differed between the two soils, and also exhibited different temperature dependence. We conclude that temperature can be an important factor regulating the community composition of methanotrophs in soil.