Nitrosomonas and Nitrobacter cause nitrification are an obligate

Nitrosomonas and Nitrobacter are chemoautotrophic organisms found in soil and water and are responsible for the oxidation of ammonium to nitrite by Nitrosomonas and nitrite to nitrate in the presence of Nitrobacter.
These are obligate autotrophs that can obtain energy only by the oxidation of inorganic substrates and that cannot assimilate simple organic substrates, such as acetate, in the same way as carbon dioxide.