Cryptic CH4 cycling in the sulfate–methane transition of marine sediments apparently mediated by ANME-1 archaea

Methane in the seabed is mostly oxidized to CO 2 with sulfate as the oxidant before it reaches the overlying water column. This microbial oxidation takes place within the sulfate–methane transition (SMT), a sediment horizon where the downward diffusive flux of sulfate encounters an upward flux of me...

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Bibliographic Details
Published in:The ISME Journal 2019-02, Vol.13 (2), p.250-262
Main Authors: Beulig, F., Røy, H., McGlynn, S. E., Jørgensen, B. B.
Format: Article
Language:English
Subjects:
45/22
45/77
631/326/47
704/172
Archaea
Biomedical and Life Sciences
Carbon dioxide
Carbon isotopes
Cycles
Ecology
Evolutionary Biology
Fluctuations
Fluxes
Genomes
Life Sciences
Marine sediments
Methane
Methanogenic bacteria
Microbial Ecology
Microbial Genetics and Genomics
Microbiology
Microorganisms
Ocean floor
Organic matter
Oxidation
Oxidizing agents
Radioactive tracers
Sediments
Stoichiometry
Sulfate reduction
Sulfates
Water column
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Summary:Methane in the seabed is mostly oxidized to CO 2 with sulfate as the oxidant before it reaches the overlying water column. This microbial oxidation takes place within the sulfate–methane transition (SMT), a sediment horizon where the downward diffusive flux of sulfate encounters an upward flux of methane. Across multiple sites in the Baltic Sea, we identified a systematic discrepancy between the opposing fluxes, such that more sulfate was consumed than expected from the 1:1 stoichiometry of methane oxidation with sulfate. The flux discrepancy was consistent with an oxidation of buried organic matter within the SMT, as corroborated by stable carbon isotope budgets. Detailed radiotracer experiments showed that up to 60% of the organic matter oxidation within the SMT first produced methane, which was concurrently oxidized to CO 2 by sulfate reduction. This previously unrecognized “cryptic” methane cycling in the SMT is not discernible from geochemical profiles due to overall net methane consumption. Sedimentary gene pools suggested that nearly all potential methanogens within and beneath the SMT belonged to ANME-1 archaea, which are typically associated with anaerobic methane oxidation. Analysis of a metagenome-assembled genome suggests that predominant ANME-1 do indeed have the enzymatic potential to catalyze both methane production and consumption.
ISSN:1751-7362
1751-7370
DOI:10.1038/s41396-018-0273-z