Nitrification is the biological process by which nitrates are produced in the environment. Nitrification occurs in two distinct stages, each under the action of different microorganisms. Step 1: Ammonia is oxidised to nitrite. This is called nitritation (the reaction by bacteria of the genus Nitrosomonas, Nitrosococcus and Nitrosospira also called nitrosation). Step 2: Nitrite is oxidised to nitrate. This is called nitration (the reaction by bacteria of the genus Nitrobacter, Nitrococcus and Nitrospira). In this process, which takes place in neutral, oxidising soils without too much organic matter (competitive heterotrophy by saprophytic bacteria), the oxidation of nitrogen by these bacteria provides them with the energy necessary to transform CO2 into organic matter (autotrophy). The toxic nitrite waste of the first bacterial community is used as a metabolite by the second one. This symbiosis phenomenon is called syntrophy.