Small group of oxygen-requiring bacteria that use nitrogen as an energy source.
These microorganisms are important in the nitrogen cycle as converters of soil ammonia to nitrates , compounds usable by plants. The nitrification process requires two distinct groups: bacteria that convert ammonia to nitrites , and bacteria that convert nitrites to nitrates. In agriculture, irrigation with dilute solutions of ammonia results in an increase in soil nitrates through the action of nitrifying bacteria. See also denitrifying bacteria .