Methane-Consuming Archaea Revealed by Directly Coupled Isotopic and Phylogenetic Analysis

Microorganisms living in anoxic marine sediments consume more than 80% of the methane produced in the world's oceans. In addition to single-species aggregates, consortia of metabolically interdependent bacteria and archaea are found in methane-rich sediments. A combination of fluorescence in situ hybridization and secondary ion mass spectrometry shows that cells belonging to one specific archaeal group associated with the Methanosarcinales were all highly depleted in ^(13)C (to values of –96‰). This depletion indicates assimilation of isotopically light methane into specific archaeal cells. Additional microbial species apparently use other carbon sources, as indicated by significantly higher ^(13)C/^(12)C ratios in their cell carbon. Our results demonstrate the feasibility of simultaneous determination of the identity and the metabolic activity of naturally occurring microorganisms