Physiological and Ecological Aspects of Aerobic Denitrification, a Link with Heterotrophic Nitrification?

Abstract

For about a century, the existence of aerobic denitrification was a subject of debate, if not controversy (Robertson & Kuenen, 1984a). However, as available technology (e.g. sensitive oxygen — analyzing equipment, chemostats, mass spectrometers) has improved, it has been possible to establish that a number of strains do indeed denitrify while simultaneously respiring oxygen. This is, of course, not true of all denitrifiers. Thiomicrospira denitrificans appears to be the most specialized as it can only tolerate oxygen in limiting concentrations. Other species, including most Paracoccus denitrificans strains, can grow under fully aerobic conditions, but only denitrify in the virtual absence of oxygen. These species fit the classical definition of denitrifiers. A third group is made up of strains which simultaneously utilize oxygen and denitrify — the aerobic denitrifiers. The members of this group do not show a uniform response to oxygen, denitrification by some of them is inhibited by relatively low amounts of oxygen (e.g. Hyphomicrobium X; Melberg et al., 1980) while others continue to denitrify even at air saturation (e.g. Thiosphaera pantotropha). It is not unlikely that, as with electron donors, the environmental conditions and nutrient supplies determine whether specialist or versatile denitrifiers occur in any given ecosystem.