Activity and community structure of methane-oxidising bacteria in a wet meadow soil

The structure and activity of the methane-oxidising microbial community in a wet meadow soil in Germany were investigated using biogeochemical, cultivation, and molecular fingerprinting techniques. Both methane from the atmosphere and methane produced in anaerobic subsurface soil were oxidised. The specific affinity (first-order rate constant) for methane consumption was highest in the top 20 cm of soil and the apparent half-saturation constant was 137-300 nM CH(4), a value intermediate to measured values in wetland soils versus well-aerated upland soils. Most-probable-number (MPN) counting of methane-oxidising bacteria followed by isolation and characterisation of strains from the highest positive dilution steps suggested that the most abundant member of the methane-oxidising community was a Methylocystis strain (10(5)-10(7) cells g(-1) d.w. soil). Calculations based on kinetic data suggested that this cell density was sufficient to account for the observed methane oxidation activity in the soil. DNA extraction directly from the same soil samples, followed by PCR amplification and comparative sequence analyses of the pmoA gene, also detected Methylocystis. However, molecular community fingerprinting analyses revealed a more diverse and dynamic picture of the methane-oxidising community. Retrieved pmoA sequences included, besides those closely related to Methylocystis spp., others related to the genera Methylomicrobium and Methylocapsa, and there were differences across samples which were not evident in MPN analyses.