title: Aerobic Microbial Respiration In Oceanic Oxygen Minimum Zones.
abstract: Oxygen minimum zones are major sites of fixed nitrogen loss in the ocean. Recent studies have highlighted the importance of anaerobic ammonium oxidation, anammox, in pelagic nitrogen removal. Sources of ammonium for the anammox reaction, however, remain controversial, as heterotrophic denitrification and alternative anaerobic pathways of organic matter remineralization cannot account for the ammonium requirements of reported anammox rates. Here, we explore the significance of microaerobic respiration as a source of ammonium during organic matter degradation in the oxygen-deficient waters off Namibia and Peru. Experiments with additions of double-labelled oxygen revealed high aerobic activity in the upper OMZs, likely controlled by surface organic matter export. Consistently observed oxygen consumption in samples retrieved throughout the lower OMZs hints at efficient exploitation of vertically and laterally advected, oxygenated waters in this zone by aerobic microorganisms. In accordance, metagenomic and metatranscriptomic analyses identified genes encoding for aerobic terminal oxidases and demonstrated their expression by diverse microbial communities, even in virtually anoxic waters. Our results suggest that microaerobic respiration is a major mode of organic matter remineralization and source of ammonium (~45-100%) in the upper oxygen minimum zones, and reconcile hitherto observed mismatches between ammonium producing and consuming processes therein.
authors.affiliation: Biogeochemistry Department, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Kalvelage
authors.affiliation: Biogeochemistry Department, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.affiliation: Biogeochemistry Department, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Marlene M
authors.initials: MM
authors.lastname: Jensen
authors.affiliation: Department of Biological Sciences, University of Aarhus, Aarhus, Denmark.
authors.forename: Niels Peter
authors.initials: NP
authors.lastname: Revsbech
authors.affiliation: Institute for General Microbiology, Christian Albrechts University Kiel, Kiel, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Löscher
authors.affiliation: Institute for General Microbiology, Christian Albrechts University Kiel, Kiel, Germany; GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Schunck
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Dhwani K
authors.initials: DK
authors.lastname: Desai
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Helena
authors.initials: H
authors.lastname: Hauss
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Kiko
authors.affiliation: Biogeochemistry Department, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Holtappels
authors.affiliation: GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
authors.forename: Julie
authors.initials: J
authors.lastname: LaRoche
authors.affiliation: Institute for General Microbiology, Christian Albrechts University Kiel, Kiel, Germany.
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Schmitz
authors.affiliation: Dirección de Investigaciones Oceanográficas, Instituto del Mar del Perú, Lima, Peru.
authors.forename: Michelle I
authors.initials: MI
authors.lastname: Graco
authors.affiliation: Biogeochemistry Department, Max Planck Institute for Marine Microbiology, Bremen, Germany.
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism*; D001420:Bacteria, Aerobic / Q000145:classification / Q000235:genetics / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000145:classification / Q000235:genetics / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D054892:Metagenome / Q000235:genetics; D009276:Namibia; D009792:Oceans and Seas; D009930:Organic Chemicals / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D010568:Peru; D012623:Seawater / Q000737:chemistry / Q000382:microbiology*; D059467:Transcriptome / Q000235:genetics
chemical_list: D064751:Ammonium Compounds; D009930:Organic Chemicals; D010088:Oxidoreductases; D003576:Electron Transport Complex IV; D010100:Oxygen