Determining the 15N and 18O isotope effects of nitrite oxidation in multiple species of nitrite-oxidizing bacteria in continuous culture

Jennifer Butler and Carolyn Buchwald, Dalhousie University, Department of Oceanography, Halifax, NS, Canada
Biologically available nitrogen (N) is fundamental for life and is a limiting nutrient in many parts of the ocean. There are many uncertainties with regards to global N budgets and the microbes that utilize these key nutrients. A significant loss of fixed N comes from oxygen deficient zones (ODZs) as denitrifying bacteria convert nitrate to nitrite and ultimately nitrogen gas anaerobically. However it is also thought that nitrite oxidizing bacteria (NOB) may play a role in the denitrification process. To help clarify what processes are occurring, dual isotope tracers of N and oxygen (O) can be used. This study is investigating aerobic nitrite oxidation by a variety of NOB grown in continuous culture to determine the associated N and O isotope effects. Species are grown at various rates to assess if growth rate has any impact on isotope effects. The isotope effects of δ15N for nitrite oxidation by Nitrococcus mobilis were found to be between -17.9‰ and -8.4‰, whereas δ18O isotope effects ranged from -4.9‰ to -1.9‰. These values are comparable to previous studies conducted in batch culture. These novel parameters have the potential to improve current stable isotope models to interpret nitrogen cycling in ODZs.