Carbon-dependent growth, community structure and methane oxidation performance of a soil-derived methanotrophic mixed culture.

Soil-borne methane-oxidizing microorganisms act as a terrestrial methane (CH4) sink and are potentially useful in decreasing global CH4 emissions. Understanding the ecophysiology of methanotrophs is crucial for a thorough description of global carbon cycling. Here, we report the in situ balance of soils from abandoned landfills, meadows and wetlands, their capacities to produce and oxidize CH4 at laboratory-scale and the isolation of a soil-borne methanotrophic-heterotrophic mixed culture that was used for carbon (C1 and C2) feeding experiments. We showed that even with similar soil properties, the in situ CH4 balance depends on land-use. Different soils had different potentials to adapt to increased CH4 availability, leading to the highest CH4 oxidation capacities for landfill and wetland soils. The most efficient mixed culture isolated from the landfill was dominated by the methanotrophs Methylobacter sp. and Methylosinus sp., which were accompanied by Variovorax sp. and Pseudomonas sp. and remained active in oxidizing CH4 when supplied with additional C-sources. The ratios between type I and type II methanotrophs and between methanotrophic and heterotrophic bacteria changed when C-sources were altered. A significant effect of the application of the mixed culture on the CH4 oxidation of soils was established but the extent varied depending on soil type.