nitrobacterium
/ˌnʌɪtrəʊbakˈtɪərɪəm/noun
Any nitrifying bacterium; especially one of the genus Nitrobacter, which oxidizes nitrites to nitrates. Usually in plural.
Origin
Late 19th century; earliest use found in Journal of the Royal Microscopical Society. From nitro- + bacterium, after French nitrobactérie.