Massive Nitrogen Loss from the Benguela Upwelling System through Anaerobic Ammonium Oxidation

• Published in: Proceedings of the National Academy of Sciences - PNAS 2005-05, Vol.102 (18), p.6478-6483
• Main Authors: Marcel M. M. Kuypers, Lavik, Gaute, Woebken, Dagmar, Schmid, Markus, Fuchs, Bernhard M., Amann, Rudolf, Jørgensen, Bo Barker, Mike S. M. Jetten, Hayes, John M.
• Format: Article
• Language: English
• Subjects: Ammonia; Atlantic Ocean; Bacteria; Bacteria, Anaerobic - genetics; Bacteria, Anaerobic - metabolism; Biological Sciences; Cloning, Molecular; Denitrification; DNA, Complementary - genetics; Gas Chromatography-Mass Spectrometry; In Situ Hybridization, Fluorescence; Lipids; Marine; Nitrates; Nitrites; Nitrogen; Nitrogen - metabolism; Nitrogen Isotopes; Oceans; Oxidation; Oxidation-Reduction; Oxygen; Oxygen - analysis; Phylogeny; Plankton; Quaternary ammonium compounds; Quaternary Ammonium Compounds - metabolism; RNA, Ribosomal, 16S - genetics; Sea water; Seawater - analysis; Seawater - microbiology; Sequence Analysis, DNA; Sodium Chloride - analysis; Temperature; Upwelling water; Water Microbiology; Water Movements
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0502088102

In many oceanic regions, growth of phytoplankton is nitrogen-limited because fixation of N2cannot 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 N2by 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 N2by 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.