title: Massive nitrogen loss from the Benguela upwelling system through anaerobic ammonium oxidation.
abstract: In many oceanic regions, growth of phytoplankton is nitrogen-limited because fixation of N2 cannot make up for the removal of fixed inorganic nitrogen (NH4+, NO2-, and NO3-) by anaerobic microbial processes. Globally, 30-50% of the total nitrogen loss occurs in oxygen-minimum zones (OMZs) and is commonly attributed to denitrification (reduction of nitrate to N2 by heterotrophic bacteria). Here, we show that instead, the anammox process (the anaerobic oxidation of ammonium by nitrite to yield N2) is mainly responsible for nitrogen loss in the OMZ waters of one of the most productive regions of the world ocean, the Benguela upwelling system. Our in situ experiments indicate that nitrate is not directly converted to N2 by heterotrophic denitrification in the suboxic zone. In the Benguela system, nutrient profiles, anammox rates, abundances of anammox cells, and specific biomarker lipids indicate that anammox bacteria are responsible for massive losses of fixed nitrogen. We have identified and directly linked anammox bacteria to the removal of fixed inorganic nitrogen in the OMZ waters of an open-ocean setting. We hypothesize that anammox could also be responsible for substantial nitrogen loss from other OMZ waters of the ocean.
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany. mkuypers@mpi-bremen.de
authors.forename: Marcel M M
authors.initials: MM
authors.lastname: Kuypers
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.forename: Dagmar
authors.initials: D
authors.lastname: Woebken
authors.forename: Markus
authors.initials: M
authors.lastname: Schmid
authors.forename: Bernhard M
authors.initials: BM
authors.lastname: Fuchs
authors.forename: Rudolf
authors.initials: R
authors.lastname: Amann
authors.forename: Bo Barker
authors.initials: BB
authors.lastname: Jørgensen
authors.forename: Mike S M
authors.initials: MS
authors.lastname: Jetten
mesh_terms: D001267:Atlantic Ocean; D001421:Bacteria, Anaerobic / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D008401:Gas Chromatography-Mass Spectrometry; D017404:In Situ Hybridization, Fluorescence; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis; D010802:Phylogeny; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000032:analysis / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D012965:Sodium Chloride / Q000032:analysis; D013696:Temperature; D014871:Water Microbiology; D014872:Water Movements
chemical_list: D018076:DNA, Complementary; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D012336:RNA, Ribosomal, 16S; D012965:Sodium Chloride; D009584:Nitrogen; D010100:Oxygen