title: Anaerobic methane oxidation coupled to denitrification is the dominant methane sink in a deep lake.
abstract: Anaerobic methane oxidation coupled to denitrification, also known as "nitrate/nitrite-dependent anaerobic methane oxidation" (n-damo), was discovered in 2006. Since then, only a few studies have identified this process and the associated microorganisms in natural environments. In aquatic sediments, the close proximity of oxygen- and nitrate-consumption zones can mask n-damo as aerobic methane oxidation. We therefore investigated the vertical distribution and the abundance of denitrifying methanotrophs related to Candidatus Methylomirabilis oxyfera with cultivation-independent molecular techniques in the sediments of Lake Constance. Additionally, the vertical distribution of methane oxidation and nitrate consumption zones was inferred from high-resolution microsensor profiles in undisturbed sediment cores. M. oxyfera-like bacteria were virtually absent at shallow-water sites (littoral sediment) and were very abundant at deep-water sites (profundal sediment). In profundal sediment, the vertical distribution of M. oxyfera-like bacteria showed a distinct peak in anoxic layers that coincided with the zone of methane oxidation and nitrate consumption, a strong indication for n-damo carried out by M. oxyfera-like bacteria. Both potential n-damo rates calculated from cell densities (660-4,890 µmol CH4⋅m(-2)⋅d(-1)) and actual rates calculated from microsensor profiles (31-437 µmol CH4⋅m(-2)⋅d(-1)) were sufficiently high to prevent methane release from profundal sediment solely by this process. Additionally, when nitrate was added to sediment cores exposed to anoxic conditions, the n-damo zone reestablished well below the sediment surface, completely preventing methane release from the sediment. We conclude that the previously overlooked n-damo process can be the major methane sink in stable freshwater environments if nitrate is available in anoxic zones.
authors.affiliation: Department of Biology, University of Constance, D-78457 Constance, Germany; Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305;
authors.forename: Joerg S
authors.initials: JS
authors.lastname: Deutzmann
authors.affiliation: Microsensor Group, Max Planck Institute for Marine Microbiology, D-28359 Bremen, Germany; and Nordic Center for Earth Evolution, Department of Biology, University of Southern Denmark, DK-5230 Odense M, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Stief
authors.affiliation: Department of Biology, University of Constance, D-78457 Constance, Germany;
authors.forename: Josephin
authors.initials: J
authors.lastname: Brandes
authors.affiliation: Department of Biology, University of Constance, D-78457 Constance, Germany; Bernhard.Schink@uni-konstanz.de.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Schink
mesh_terms: D000693:Anaerobiosis; D058440:Denitrification; D019015:Geologic Sediments; D060106:Lakes; D008697:Methane / Q000737:chemistry*; D010084:Oxidation-Reduction
chemical_list: D008697:Methane
keywords: Lake Constance; M. oxyfera-like bacteria; NC-10 bacteria; microsensor profiles; n-damo