Autotrophic Nitrification in Bacteria

This chapter highlights the physiology of autotrophic ammonia- and nitrite-oxidizing bacteria. Several aspects of the physiology of nitrifiers of relevance to their growth and activity in natural environments are considered. The chapter describes the basic features of the biochemistry of ammonia and nitrite oxidation and discusses the growth limiting factors and activity of these organisms. The influence of oxygen concentration, pH value, and inhibitors on their physiology is also described. Nitrification plays a central role in the nitrogen cycle of terrestrial and aquatic ecosystems, converting the most reduced form of nitrogen, NH3, to the most oxidized form, NO3. Nitrifying bacteria occupy niches in many ecosystems and compete successfully with faster and more efficiently growing organisms for oxygen, ammonia, and carbon dioxide. Nitrifiers are capable of reversing the nitrification process, carrying out denitrification and producing nitrite, ammonia, nitrous and nitric oxides, and gaseous nitrogen. Ammonia oxidizers can metabolize urea and can assimilate carbon from methane while nitrite oxidizers can grow anaerobically in the presence of organic compounds and nitrate.