HR: 0800h
AN: B21A-0861    [Abstracts]
TI: Using Pure Cultures to Define the Site Preference of Nitrous Oxide Produced by Microbial Nitrification and Denitrification
AU: * Sutka, R L
EM: sutkarob@msu.edu
AF: Department of Zoological Sciences, Michigan State University 203 Natural Sciences, East Lansing, MI 48824 United States
AU: Breznak, J A
EM: breznak@msu.edu
AF: Department of Microbiology and Molecular Genetics, Michigan State University 6190 Biomedical and Physical Sciences Building, East Lansing, MI 48824 United States
AU: Ostrom, N E
EM: ostromn@msu.edu
AF: Department of Zoological Sciences, Michigan State University 203 Natural Sciences, East Lansing, MI 48824 United States
AU: Ostrom, P H
EM: ostrom@msu.edu
AF: Department of Zoological Sciences, Michigan State University 203 Natural Sciences, East Lansing, MI 48824 United States
AU: Gandhi, H
EM: gandhiha@msu.edu
AF: Department of Zoological Sciences, Michigan State University 203 Natural Sciences, East Lansing, MI 48824 United States
AB: Defining the site preference of nitrous oxide (N$_{2}$O) produced in pure culture studies is crucial to interpreting field data. We have previously demonstrated that the intramolecular distribution of nitrogen isotopes (isotopomers) can be used to differentiate N$_{2}$O produced by nitrifier denitrification and nitrification in cultures of Nitrosomonas europaea. Here, we have expanded on our initial results and evaluated the isotopomeric composition of N$_{2}$O produced during nitrification and nitrifier denitrification with cultures of Nitrosospira multiformis. In addition, we have analyzed N$_{2}$O produced during methanotrophic nitrification, denitrification, and fungal denitrification. To evaluate N$_{2}$O production during nitrification and nitrifier denitrification, we compared the site preference of N$_{2}$O formed as a result of nitrite reduction and hydroxylamine oxidation with {\it Nitrosomonas europaea} and {\it Nitrosospira multiformis}. The average site preference of N$_{2}$O produced by hydroxylamine oxidation was similar for {\it Nitrosomonas europaea} (33.0 $\pm$ 3.5 $\permil$) and {\it Nitrosospira multiformis} (33.1 $\pm$ 4.2 $\permil$). Nitrous oxide produced by nitrifier-denitrification by {\it Nitrosomonas europaea} and {\it Nitrosospira multiformis} had a similar site preference of - 1.4 $\pm$ 4.4 $\permil$ and - 1.1 $\pm$ 2.6 $\permil$ respectively. The results indicate that it is possible to differentiate between N$_{2}$O produced by nitrite reduction and hydroxylamine oxidation by ammonia oxidizing bacteria. Methanotrophic nitrification was evaluated by analyzing the N$_{2}$O produced during hydroxylamine oxidation in concentrated cell suspensions of two methane oxidizing bacteria. The site preference of N$_{2}$O produced by the two methane oxidizers, {\it Methylococcus capsulatus} Bath and {\it Methylosinus trichosporium} was 31.8 $\pm$ 4.7 $\permil$ and 33.0 $\pm$ 4.5 $\permil$ respectively. The results indicate that a site preference of 33 $\permil$ is applicable for nitrification regardless of whether a methane oxidizer or ammonia oxidizer is involved in the reaction. To determine the site preference of N$_{2}$O produced during denitrification we used concentrated cell suspensions of two organisms ({\it Pseudomonas chlororaphis} and {\it Pseudomonas aureofaciens}) that lack N$_{2}$O reductase. The site preference of N$_{2}$O produced during nitrite reduction was similar for {\it P. chlororaphis} (0.3 $\pm$ 2.7 $\permil$) and P. aureofaciens (- 0.3 $\pm$ 1.7 $\permil$ ). The results indicate that the site preference of N$_{2}$O produced during nitrite reduction is 0 $\permil$ regardless of whether the organism is a denitrifier or nitrifier. Fungal denitrification was investigated using pure cultures of {\it Fusarium oxysporum} and {\it Cylindrocarpon tonkinense}. The site preference of N$_{2}$O produced during nitrite reduction was similar for the cultures with an average site preference of 34.7 $\pm$ 2.2 $\permil$ for {\it Fusarium oxysporum} and 29.7 $\pm$ 1.7 $\permil$ for {\it Cylindrocarpon tonkinense}. The data indicate that fungal denitrification and bacterial denitrification can be distinguished based on site preference. The results from all of the pure culture studies indicate that isotopomers can be used to apportion bacterial nitrification and denitrification and in field studies.
DE: 1040 Isotopic composition/chemistry
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 0330 Geochemical cycles
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting