Nitrification

Nitrification is an autotrophic process during which bacteria couple energy release from the oxidation of ammonium with the biosynthesis of simple inorganic molecules such as carbon dioxide and water into organic compounds. Because chemical energy is being tapped by the bacteria, nitrification is known as a chemoautotrophic process rather than photoautotrophic, as when green plants utilize sunlight in their photosynthetic productivity.

Only a few types of aerobic bacteria are capable of performing the chemical reactions of nitrification. The first step in nitrification is the oxidation of ammonium to nitrite. This function is mostly carried out by bacteria in the genus Nitrosomonas, with lesser activity by the genera Nitrosospira, Nitrosococcus, and Nitrosolobus. The nitrite formed by these bacteria does not accumulate in soil because it is rapidly oxidized to nitrate. This stage is mostly accomplished by bacteria in the genus Nitrobacter, along with Nitrosospira and Nitrosococcus.