title: Denitrifying bacteria anaerobically oxidize methane in the absence of Archaea.
abstract: Recently, a microbial consortium was shown to couple the anaerobic oxidation of methane to denitrification, predominantly in the form of nitrite reduction to dinitrogen gas. This consortium was dominated by bacteria of an as yet uncharacterized division and archaea of the order Methanosarcinales. The present manuscript reports on the upscaling of the enrichment culture, and addresses the role of the archaea in methane oxidation. The key gene of methanotrophic and methanogenic archaea, mcrA, was sequenced. The associated cofactor F(430) was shown to have a mass of 905 Da, the same as for methanogens and different from the heavier form (951 Da) found in methanotrophic archaea. After prolonged enrichment (> 1 year), no inhibition of anaerobic methane oxidation was observed in the presence of 20 mM bromoethane sulfonate, a specific inhibitor of MCR. Optimization of the cultivation conditions led to higher rates of methane oxidation and to the decline of the archaeal population, as shown by fluorescence in situ hybridization and quantitative MALDI-TOF analysis of F(430). Mass balancing showed that methane oxidation was still coupled to nitrite reduction in the total absence of oxygen. Together, our results show that bacteria can couple the anaerobic oxidation of methane to denitrification without the involvement of Archaea.
authors: Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, The Netherlands.
authors: Katharina F
authors: KF
authors: Ettwig
authors: Seigo
authors: S
authors: Shima
authors: Katinka T
authors: KT
authors: van de Pas-Schoonen
authors: Jörg
authors: J
authors: Kahnt
authors: Marnix H
authors: MH
authors: Medema
authors: Huub J M
authors: HJ
authors: Op den Camp
authors: Mike S M
authors: MS
authors: Jetten
authors: Marc
authors: M
authors: Strous
mesh_terms: D001105:Archaea / Q000201:enzymology / Q000235:genetics; D019843:Archaeal Proteins / Q000235:genetics; D008697:Methane / Q000378:metabolism*; D019640:Methanosarcinales / Q000378:metabolism*; D008969:Molecular Sequence Data; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010084:Oxidation-Reduction; D017422:Sequence Analysis, DNA
chemical_list: D019843:Archaeal Proteins; D009573:Nitrites; D009584:Nitrogen; D008697:Methane