Metabolismus und Biomineralisation in anaerob Methan-oxidierenden Lebensgemeinschaften

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Anaerobic oxidation of methane (AOM) is recognized as one key process of methane consumption in oceans. According to phylogenetic and metagenomic analyses, the process is carried out by syntrophic consortia of anaerobic methanotrophic archaea and sulfate reducing bacteria. Here, a more comprehensive view inside methanotrophic consortia from anoxic Black Sea cold seeps is shown. By using a set of antibodies as markers, the metabolic activity of the syntrophic partners could be identified. The key enzymes methyl coenzyme M reductase of the (reverse) methanogenic pathway and APS reductase (sulfate reduction pathway) were detected on cellular and subcellular level. Intriguingly, active methylotrophic bacteria, known for aerobic methane oxidation, could be detected in the anoxic environment by the expressed methanol dehydrogenase. It was shown that aerobic as well as anaerobic methane oxidation occur simultaneously, several tens of micrometers apart, in a complex, redox-stratified consortium. The results confirm the syntrophic AOM as dominant process in these anoxic environments and suggest, at the same time, the overall importance of aerobic methanotrophy, since it is not limited to oxic zones of the oceans. Moreover, a terrestrial site of methane emission was focused in this work. The diversity of prokaryotic organisms involved in oxidation of methane was investigated in fluid samples from the Salse di Nirano mud volcano field situated in the Northern Apennines (Italy). Cell counts were at approximately 0.7 x 106 microbial cells/ml. By fluorescence in situ hybridization analysis a fraction of the microbial biomass was identified as ANME archaea associated in densely populated flakes, of some tens of µm in diameter, embedded in a hyaline matrix. Diversity analysis based on the 16S rDNA genes, revealed a high proportion of archaea, involved in sulfate-dependent as well as suggested iron-manganese-dependent AOM. Aerobic methane-oxidizing Proteobacteria could be highly enriched from mud volcano fluids, indicating the presence of aerobic methanotrophic bacteria, which may contribute to methane oxidation, whenever oxygen is readily available. The results imply that biofilms, dominated by ANME archaea, colonize deeply buried parts of the mud volcano venting system.