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

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.