Fractionation of N2O isotopomers during production by denitrifier

Cultures were incubated in a batch mode with a liquid medium that contains KNO3 as unique nitrogen supply under acetylene/helium (10% v/v) atmosphere at 27 °C. Enrichment factors for 15N in bulk nitrogen in N2O (average for Nα and Nβ) fluctuated in a few tens permil showing a slight difference between the species. In contrast, 15N-site preference (difference in isotope ratios between Nα and Nβ) showed nearly constant and distinct value for the two species (23.3±4.2 and −5.1±1.8‰ for P. fluorescens and P. denitrificans, respectively). The site preference was also measured for N2O produced by inorganic reactions (nitrite reduction and hydroxylamine oxidation); a unique value (about 30‰ for the both reactions) was obtained. These results and those recently reported for nitrifying bacteria suggest that 15N-site preference in N2O can be used to identify the production processes of N2O on the level of bacterial species or enzymes involved.