title: Methane oxidation coupled to nitrate reduction under hypoxia by the Gammaproteobacterium Methylomonas denitrificans, sp. nov. type strain FJG1.
abstract: Obligate methanotrophs belonging to the Phyla Proteobacteria and Verrucomicrobia require oxygen for respiration and methane oxidation; nevertheless, aerobic methanotrophs are abundant and active in low oxygen environments. While genomes of some aerobic methanotrophs encode putative nitrogen oxide reductases, it is not understood whether these metabolic modules are used for NOx detoxification, denitrification or other purposes. Here we demonstrate using microsensor measurements that a gammaproteobacterial methanotroph Methylomonas denitrificans sp. nov. strain FJG1(T) couples methane oxidation to nitrate reduction under oxygen limitation, releasing nitrous oxide as a terminal product. Illumina RNA-Seq data revealed differential expression of genes encoding a denitrification pathway previously unknown to methanotrophs as well as the pxmABC operon in M. denitrificans sp. nov. strain FJG1(T) in response to hypoxia. Physiological and transcriptome data indicate that genetic inventory encoding the denitrification pathway is upregulated only upon availability of nitrate under oxygen limitation. In addition, quantitation of ATP levels demonstrates that the denitrification pathway employs inventory such as nitrate reductase NarGH serving M. denitrificans sp. nov. strain FJG1(T) to conserve energy during oxygen limitation. This study unravelled an unexpected metabolic flexibility of aerobic methanotrophs, thereby assigning these bacteria a new role at the metabolic intersection of the carbon and nitrogen cycles.
authors.affiliation: Department of Biological Sciences, University of Alberta, CW405, Biological Sciences Building, Edmonton, AB, T6G 2E9, Canada.
authors.forename: K Dimitri
authors.initials: KD
authors.lastname: Kits
authors.affiliation: Department of Biological Sciences, University of North Carolina, 9201 University City Boulevard, Charlotte, NC, 28223, USA.|Institute of Marine Microbes and Ecospheres and State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, 361005, China.
authors.forename: Martin G
authors.initials: MG
authors.lastname: Klotz
authors.affiliation: Department of Biological Sciences, University of Alberta, CW405, Biological Sciences Building, Edmonton, AB, T6G 2E9, Canada.
authors.forename: Lisa Y
authors.initials: LY
authors.lastname: Stein
mesh_terms: D000693:Anaerobiosis; D058440:Denitrification / Q000235:genetics; D008697:Methane / Q000378:metabolism*; D020620:Methylomonas / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D050901:Nitrate Reductase / Q000235:genetics; D009566:Nitrates / Q000378:metabolism*; D009609:Nitrous Oxide / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics; D010100:Oxygen / Q000378:metabolism*; D010802:Phylogeny
chemical_list: D009566:Nitrates; D010088:Oxidoreductases; C022763:nitrous oxide reductase; D050901:Nitrate Reductase; D009609:Nitrous Oxide; D008697:Methane; D010100:Oxygen