*FMIILY I. NITROBACTERIACEAE BUCHANAN 

 (Jour. Bact., 2, 1917, 349 and Jour. Bact., 3, 1918, 179.) 



Cells without endospores. Rod-shaped or ellipsoidal except for one spherical spe- 

 cies (Xitrosococcus riitrosus). Spiral rods in A'itrosospira and in one species of 

 Thiobacillus. Flagella either polar (so far as known), or absent. Gram stain un- 

 certain, but presumably Gram-negative for all of the polar flagellate, rod-shaped 

 species except for Nitrosomonas monocella which is reported to be Gram-positive. 

 Capable of growing without organic compounds, using CO2 as the source of carbon, 

 and obtaining their energy by oxidation of ammonia, nitrite, hydrogen, sulfur, or 

 thiosulfate. Some species can also utilize organic compounds. Non-parasitic, 

 usually soil or water forms. 



Key to the tribes and genera of family Nitrobacteriaceae. 



A. Organisms oxidize ammonia to nitrite, or nitrite to nitrate. Growth on stand- 

 ard media very poor or absent. 



Tribe I. Nitrobacterieae, p. 70. 

 a. Cells oxidize ammonia to nitrite. 



b. Cells are separate, free or in dense aggregates. Do not form zoogloea. 

 c. Cells ellipsoidal. 



Genus I. Nitrosomonas, p. 70. 



cc. Cells spherical, 

 ccc. Cells spiral. 



Genus II. A'itrosococcus, p. 71. 

 Genus III. Nilrosospira, p. 71. 



bb. Cells form a zoogloea. 



c. The zoogloea is surrounded by a common membrane forming a 

 cyst. 



Genus IV. Nitrosocystis, p. 72. 

 cc. The massed cells are embedded in slime. No common membrane 

 surrounds the cells. 



Genus V. Nitrosogloea, p. 73. 

 aa. Cells oxidize nitrite to nitrate. 

 b. Cells form no zoogloea. 



Genus VI. Niirobacter, p. 74. 

 bb. Cells form a zoogloea. 



Genus VII. Nitrocystis, p. 75. 

 B. Organisms oxidize hydrogen. 



Tribe II. Hydrogenomonadeae, p. 76. 

 a. Aerobic, non-spore-forming rods with single polar flagellum, or non-motile. 



Genus I. Hydrogenomonas , p. 76. 



* Text revised by Prof. R. S. Breed and Prof. H. J. Conn, Geneva, N. Y., Dec, 

 1937. Completely revised by Dr. R. L. Starkey, New Jersey Agricultural Experiment 

 Station, New Brunswick, N. J., March, 1943. 



69 



