title: Diatoms respire nitrate to survive dark and anoxic conditions.
abstract: Diatoms survive in dark, anoxic sediment layers for months to decades. Our investigation reveals a correlation between the dark survival potential of marine diatoms and their ability to accumulate NO(3)(-) intracellularly. Axenic strains of benthic and pelagic diatoms that stored 11-274 mM NO(3)(-) in their cells survived for 6-28 wk. After sudden shifts to dark, anoxic conditions, the benthic diatom Amphora coffeaeformis consumed 84-87% of its intracellular NO(3)(-) pool within 1 d. A stable-isotope labeling experiment proved that (15)NO(3)(-) consumption was accompanied by the production and release of (15)NH(4)(+), indicating dissimilatory nitrate reduction to ammonium (DNRA). DNRA is an anaerobic respiration process that is known mainly from prokaryotic organisms, and here shown as dissimilatory nitrate reduction pathway used by a eukaryotic phototroph. Similar to large sulfur bacteria and benthic foraminifera, diatoms may respire intracellular NO(3)(-) in sediment layers without O(2) and NO(3)(-). The rapid depletion of the intracellular NO(3)(-) storage, however, implies that diatoms use DNRA to enter a resting stage for long-term survival. Assuming that pelagic diatoms are also capable of DNRA, senescing diatoms that sink through oxygen-deficient water layers may be a significant NH(4)(+) source for anammox, the prevalent nitrogen loss pathway of oceanic oxygen minimum zones.
authors.affiliation: Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany. akamp@mpi-bremen.de
authors.forename: Anja
authors.initials: A
authors.lastname: Kamp
authors.forename: Dirk
authors.initials: D
authors.lastname: de Beer
authors.forename: Jana L
authors.initials: JL
authors.lastname: Nitsch
authors.forename: Gaute
authors.initials: G
authors.lastname: Lavik
authors.forename: Peter
authors.initials: P
authors.lastname: Stief
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000641:Ammonia / Q000378:metabolism; D000693:Anaerobiosis; D003624:Darkness; D017377:Diatoms / Q000378:metabolism / Q000502:physiology*; D007553:Isotope Labeling; D009566:Nitrates / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000378:metabolism; D010084:Oxidation-Reduction; D016019:Survival Analysis
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D000641:Ammonia