Nitrifying bacteria (one of the chemosynthetic bacteria) oxidise ammonia to nitrites and obtain energy for the preparation of food. This oxidation occurs in two steps. In the first step, ammonia is oxidised to nitrite by nitrite bacteria (e.g., Nitrosomonas and Nitrococcus). In the second step, nitrite is oxidised to nitrate by nitrate bacteria (e.g., Nitrocystis and Nitrobacter).