ABSTRACT
Abstract The biological nitrogen cycle is a complex interplay between many microorganisms catalyzing different reactions. The ammonia and nitrite oxidizing bacteria that were thought to be chemolithoautotrophic were placed into the family Nitrobacteraceae. For a long time, the oxidation of the inorganic nitrogen compounds ammonia and nitrite by nitrifiers was thought to be restricted to oxic environments, and the metabolic flexibility of these organisms seemed to be limited. The discovery of a novel pathway for anaerobic ammonia oxidation by Planctomyces (anammox) and the finding of an anoxic metabolism by “classical” nitrifiers showed that these assumptions are no longer valid.
