AME 80:289-300 (2017)  -  DOI:

Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates

Juliane Jacob1,2,*, Boris Nowka3, Véronique Merten4, Tina Sanders1, Eva Spieck3, Kirstin Dähnke1

1Helmholtz Center Geesthacht, Institute of Coastal Research, Max-Planck-Str. 1, 21502 Geesthacht, Germany
2Institute of Biogeochemistry and Marine Chemistry, University of Hamburg, Bundesstr. 55, 20146 Hamburg, Germany
3Biozentrum Klein Flottbek, Department of Microbiology and Biotechnology, University of Hamburg, Ohnhorststr. 18, 22609 Hamburg, Germany
4GEOMAR Helmholtz Center for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany
*Corresponding author:

ABSTRACT: Nitrification, the step-wise oxidation of ammonium to nitrite and nitrate, is important in the marine environment because it produces nitrate, the most abundant marine dissolved inorganic nitrogen (DIN) component and N-source for phytoplankton and microbes. This study focused on the second step of nitrification, which is carried out by a distinct group of organisms, nitrite-oxidizing bacteria (NOB). The growth of NOB is characterized by nitrite oxidation kinetics, which we investigated for 4 pure cultures of marine NOB (Nitrospina watsonii 347, Nitrospira sp. Ecomares 2.1, Nitrococcus mobilis 231, and Nitrobacter sp. 311). We further compared the kinetics to those of non-marine species because substrate concentrations in marine environments are comparatively low, which likely influences kinetics and highlights the importance of this study. We also determined the isotope effect during nitrite oxidation of a pure culture of Nitrospina (Nitrospina watsonii 347) belonging to one of the most abundant marine NOB genera, and for a Nitrospira strain (Nitrospira sp. Ecomares 2.1). The enzyme kinetics of nitrite oxidation, described by Michaelis-Menten kinetics, of 4 marine genera are rather narrow and fall in the low end of half-saturation constant (Km) values reported so far, which span over 3 orders of magnitude between 9 and >1000 µM NO2-. Nitrospina has the lowest Km (19 µM NO2-), followed by Nitrobacter (28 µM NO2-), Nitrospira (54 µM NO2-), and Nitrococcus (120 µM NO2-). The isotope effects during nitrite oxidation by Nitrospina watsonii 347 and Nitrospira sp. Ecomares 2.1 were 9.7 ± 0.8 and 10.2 ± 0.9‰, respectively. This confirms the inverse isotope effect of NOB described in other studies; however, it is at the lower end of reported isotope effects. We speculate that differences in isotope effects reflect distinct nitrite oxidoreductase (NXR) enzyme orientations.

KEY WORDS: Nitrification · Nitrite-oxidizing bacteria · Isotope effect · Enzyme kinetics · Marine environment

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Cite this article as: Jacob J, Nowka B, Merten V, Sanders T, Spieck E, Dähnke K (2017) Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates. Aquat Microb Ecol 80:289-300.

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