Identification of carbon and nitrogen assimilating microbial populations in anaerobically methane-oxidising mats by stable isotope probing

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The anaerobic oxidation of methane (AOM) is a major process in the regulation of methane emissions from marine systems. There is strong evidence that AOM is carried out by a novel group of Archaea (ANME) related to methanogenic Archaea, which often occurs in close physical associations with sulphate-reducing prokaryotes (SRP). However, there are still no pure cultures of anaerobic methanotrophic microorganisms available. Consequently, fundamental aspects of the process, like its mechanism, possible intermediates, and the identity of all microbial groups involved remain unknown. Recently, a first stable isotope labelling experiment was successfully accomplished with microbial AOM-mats from the Black Sea by our group, which showed the uptake of the 13C-methane into lipid biomarkers.Clearly, a key to the understanding of the metabolic interactions and interdependencies in the different mat ecosystems necessitates a better understanding of assimilatory carbon and nitrogen fluxes. Therefore, our project will elucidate assimilative capabilities within anaerobically methaneoxidizing microbial mat communities using a suite of stable carbon and nitrogen isotope probing approaches. We will employ nucleic acid and lipid biomarker analysis to unveil carbon sinks and sources and the role of different N-compounds as nitrogen sources or for respiratory processes in the mat. This will allow to reveal assimilatory pathways, and simultaneously will enable us to identify the dominant active microbial groups involved. Ultimately, the goals are to understand the role of individual microorganisms for the methane-dependent chemosynthetic mat ecosystem and to relate patterns of carbon assimilation of individual microorganisms in the microbial mat to possible mechanisms of anaerobic methane oxidation.