Community composition and ultrastructure of a continuous bioreactor enrichment culture, in which anaerobic methane oxidation (AOM) was coupled to nitrate reduction.

Community composition and ultrastructure of a continuous bioreactor enrichment culture, in which anaerobic methane oxidation (AOM) was coupled to nitrate reduction. The biomass consisted of aggregates that were dominated by nitrate-dependent anaerobic methane-oxidizing Methanoperedens-like archaea (40%) and nitrite-dependent anaerobic methane-oxidizing Methylomirabilis-like bacteria (50%). The Methanoperedens sp. aggregates consisted of slightly irregular coccoid cells (~1.5 µm diameter) which produced extruding tubular structures and putative cell-to-cell contacts. Methylomirabilis sp. bacteria exhibited the polygonal cell shape typical of this genus. In AOM archaea and bacteria cytochrome c proteins were localized in the cytoplasm and periplasm respectively by cytochrome staining. For the first time the cell structure of anaerobic methane-oxidizing Methanoperedens sp. was revealed. Our results indicate that AOM bacteria and archaea might work closely together in the process of anaerobic methane oxidation.