Background
In 1971, Watson classified ammonia-oxidizing bacteria into four genera based upon morphology, fine structure, and percentage of guanine-cytosine (GC) within genome of 27 strains of nitrying bacteria. Nitrosomonas and Nitrosocystis species form one group, both of them belong to gammaproteobacteria. Nitrosolobus and Nitrosospira form another group; both of these belong to betaproteobacteria. Later this classification wass confirmed by 16S rRNA sequence (Head 1993, Purkhold 2000). The sequence of amo and pmo genes are also utilized to build the phylogenetic tree (Purkhold 2000)
Nitrosococcus halophilus is the closet related species to Nitrosococcus oceani. Among other cultivated aerobic AOB, N.oceani and N. halophilus are the only two organisms that are gammaproteobacterial AOB, the rest are Betaproteobacteial AOB. Nitrosococcus oceani resides in saline environment, found in marine world or seawater. Its presence is detected using immunofluoresence and FISH. (Klotz 2006))
Structure and Metabolism