Nitrification is a process in which ammonia is oxidized to nitrate under aerobic conditions under the action of inorganic nitrifying bacteria. It produces oxidized nitrate, and the product can participate in denitrification. It is a productive process, in which nitrifying bacteria synthesize cell materials by recycling CO2 through calvin cycle and incomplete tricarboxylic acid.

Denitrification is the reduction of respiratory hydrochloride to gaseous N2O and N2. It belongs to alienated nitrate reduction. Most of them are done by facultative anaerobic bacteria. It is a process of coupling to generate energy, but the electron transfer chain is short and only two ATP are produced.

Generally speaking, nitrification is used to synthesize substances in metabolism, and these bacteria are autotrophic; Denitrification decomposes substances. Most of these bacteria are heterotrophic, and a few are facultative heterotrophic or autotrophic.