The Collaborative International Dictionary of English v.0.48:

Nitrobacteriaceae \Nitrobacteriaceae\ prop. n.
   A natural family of usually rod-shaped bacteria that oxidize
   ammonia or nitrites: nitrobacteria.

   Syn: family Nitrobacteriaceae.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Nitrobacteriaceae
    n 1: usually rod-shaped bacteria that oxidize ammonia or
         nitrites: nitrobacteria [syn: Nitrobacteriaceae, family
         Nitrobacteriaceae]