Nitrifier

noun

1. Anything which serves to bring about or to facilitate the production of niter or nitrates; specifically, in bacteriology, any micro-organism which is capable of oxidizing ammonia to nitrous acid, or nitrous acid to nitric acid; a micro-organism which serves to fix, and accumulate in the soil, the free nitrogen of the air. See nitrogen-fixing.
2. An agent employed in nitrification.
3. An agent employed in nitrification.