68 ORDER I. PSEUDOMONADALES 



FAMILY I. NITROBACTERACEAE BUCHANAN, 1917.* 

 (Jour. Bact., 2, 1917, 349 and Jour. Bact., S, 1918, 179.) 



Ni.tro.bac.te.ra'ce.ae. M.L. A^ z'^rofeacier name of type genus of the family; -aceae ending 

 to denote a family; M.L. plural noun Nitrohacteraceae the Nitrobacter family. 



Cells without endospores; rod-shaped, ellipsoidal or even spherical (Nitrosococcus) or 

 spirillar in shape (Nitrosospira) . Flagella polar, occasionally absent. Gram-negative. Or- 

 ganisms which derive energy from the oxidation of ammonia to nitrite or from the oxida- 

 tion of nitrite to nitrate; these bacteria depend on this oxidation for growth and fail to grow 

 on media containing organic matter in the absence of the specific inorganic materials used 

 as sources of energy. Many organic compounds commonly used in standard culture media 

 are toxic to these bacteria. Not parasitic. Commonly found in soil and fresh water. 



The type genus for the family is Nitrobacter Winogradsky. 



As it appears to be a more logical arrangement, the genera that include the species that 

 oxidize ammonia are discussed first although the type genus does not belong in this group. 



Key to the genera of family Nitrohacteraceae. 



I. Ammonia oxidized to nitrite. 



A. Zoogloeae not formed. Cells occur separately, free or in dense aggregates. 



1. Cells not spiral -shaped. 



a. Cells ellipsoidal. 



Genus I. Nitrosomonas, p. 68. 

 aa. Cells spherical. 



Genus II. Nitrosococcus, p. 69. 



2. Cells spiral. 



Genus III. Nitrosospira, p. 70. 



B. Zoogloeae formed. 



1. Zoogloea surrounded by a common membrane forming a cyst. 



Genus IV. Nitrosocystis, p. 70. 



2. No common membrane surrounds the cells. The massed cells are embedded in 

 slime. 



Genus V. Nitrosogloea, p. 71. 

 II. Nitrite oxidized to nitrate. 



A. Zoogloeae not formed. 



Genus VI. Nitrobacter, p. 72. 



B. Zoogloeae formed. 



Genus VII. Nitrocystis, p. 73. 



Genus I. Nitrosomonas Winogradsky , 1890. 



{Nitromonas Winogradsky, Ann. Inst. Past., 4, 1890, 257; not Nitromonas Orla-Jensen, 

 Cent. f. Bakt., II Abt., 22, 1909, 334; Arch. Sci. biol., St. Petersburg, 1, 1892, 127; emend. 

 S. and H. Winogradsky, Ann. Inst. Past., 50, 1933, 393.) 



Ni.tro.so.mo'nas. M.L. nitrosus nitrous; Gr. monas, monadis a unit, monad; M.L. fem.n. 

 Nitrosomonas nitrous monad, i.e., the monad producing nitrite. 



Cells ellipsoidal, non-rhotile or with a single polar flagellum, occurring singly, in pairs, 

 short chains or irregular masses which are not enclosed in a common membrane. O.xidize 

 ammonia to nitrite more rapidly than the other genera of this family. 



The type species is Nitrosomonas europaea Winogradsky. 



* Completely revised by Dr. R. L. Starkey, New Jersey Agricultural Experiment Station, 

 New Brunswick, N. J., March, 1943; minor revisions, November, 1953. 



