Persistence of bacterial denitrification capacity under aerobic conditions: The rule rather than the exception

Bacterial decomposition of nitrate to dinitrogen and oxides of nitrogen, essential steps in the nitrogen cycle, are regarded as predominantly anaerobic processes. However, here we have shown, using simultaneous mass spectrometric monitoring of dissolved N₂, NO_x and O₂, that in the laboratory a number of different bacteria can denitrify, even when O₂ concentrations approach or exceed air saturation values. The proportions of gaseous end products vary from one organism to another and depend on the level of dissolved O₂. We, therefore, suggest that aerobic bacterial denitrification, with the production of N₂ and/or NO_x, may, contrary to the beliefs of many, be as widespread and ecologically important as its anaerobic counterpart.