title: N and O isotope fractionation in nitrate during chemolithoautotrophic denitrification by Sulfurimonas gotlandica.
abstract: Chemolithoautotrophic denitrification is an important mechanism of nitrogen loss in the water column of euxinic basins, but its isotope fractionation factor is not known. Sulfurimonas gotlandica GD1(T), a recently isolated bacterial key player in Baltic Sea pelagic redoxcline processes, was used to determine the isotope fractionation of nitrogen and oxygen in nitrate during denitrification. Under anoxic conditions, nitrate reduction was accompanied by nitrogen and oxygen isotope fractionation of 23.8 ± 2.5‰ and 11.7 ± 1.1‰, respectively. The isotope effect for nitrogen was in the range determined for heterotrophic denitrification, with only the absence of stirring resulting in a significant decrease of the fractionation factor. The relative increase in δ(18)ONO3 to δ(15)NNO3 did not follow the 1:1 relationship characteristic of heterotrophic, marine denitrification. Instead, δ(18)ONO3 increased slower than δ(15)NNO3, with a conserved ratio of 0.5:1. This result suggests that the periplasmic nitrate reductase (Nap) of S. gotlandica strain GD1(T) fractionates the N and O in nitrate differently than the membrane-bound nitrate reductase (Nar), which is generally prevalent among heterotrophic denitrifiers and is considered as the dominant driver for the observed isotope fractionation. Hence in the Baltic Sea redoxcline, other, as yet-unidentified factors likely explain the low apparent fractionation.
authors.affiliation: Leibniz Institute for Baltic Sea Research Warnemünde (IOW) , Seestrasse 15, 18119 Rostock, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Frey
authors.forename: Susanna
authors.initials: S
authors.lastname: Hietanen
authors.forename: Klaus
authors.initials: K
authors.lastname: Jürgens
authors.forename: Matthias
authors.initials: M
authors.lastname: Labrenz
authors.forename: Maren
authors.initials: M
authors.lastname: Voss
mesh_terms: D005591:Chemical Fractionation; D052837:Chemoautotrophic Growth; D058440:Denitrification; D020565:Epsilonproteobacteria / Q000378:metabolism*; D009566:Nitrates / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D009587:Nitrogen Isotopes; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000494:pharmacology; D010103:Oxygen Isotopes
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D009584:Nitrogen; D010100:Oxygen