Enrichment and identification of methane-oxidizing bacteria by using down-flow hanging sponge bioreactors under low methane concentration

Abstract

Aerobic methanotrophs in soils are an important biological sink for atmospheric methane but bacteria oxidizing atmospheric methane largely resist isolation. Here, we enriched methane-oxidizing bacteria in continuous down-flow hanging sponge (DHS) bioreactors under low methane concentration (ca. 200 ppmv) at pH 8 and 5.5, from neutral and acidic garden soil inoculum. After 3-4 months of enrichment cultivation, pmoA gene-based community analysis and kinetic experiments demonstrated that, at both pH levels, methanotrophic enrichment cultures were dominated by Methylocystis species with high apparent affinity, even though individual reactors were inoculated with different soils containing divergent methanotrophic communities. Methane concentration is likely to have a strong influence on the composition of methanotrophic communities under enrichment culture conditions. © Springer-Verlag and the University of Milan 2010.