FAMILY I. AZOTOBACTERACEAE 



283 



FAMILY I. AZOTOBACTERACEAE BERGEY, BREED AND MURRAY, 1938.* 



(Azotobacleriaceae (sic) Bergey, Breed and Murray, Preprint, Manual, 5th ed., 

 October, 1938, v and 71.) 



A.zo.to.bac.te.ra'ce.ae. M.L. mas.n. Azotobacter tj-pe genus of the familj^; -aceae end- 

 ing to denote a family; M.L. fem.pl.n. Azotobacteraceae the Azotobacter family. 



Relatively large rods or even cocci, sometimes almost yeast-like in appearance. Cells 

 without endospores. The type of flagellation in this genus has been definitely established 

 as peritrichous. Gram-negative. Obligate aerobes, usually growing in a film on the surface 

 of the culture medium. Capable of fixing atmospheric nitrogen when provided with carbo- 

 hydrate or other energy source. Grow best on media deficient in nitrogen. Soil and water 

 bacteria. 



There is a single genus. 



Genus I. Azotobacter Beijerinck, 1901. 

 (Cent. f. Bakt., II Abt., 7, 1901, 567.) 



A.zo.to.bac'ter. Gr. adj. azons without life; Fr. noun azote nitrogen; M.L. mas.n, bacter 

 the masculine equivalent of Gr. neut.n. bactrum a rod or staff; M.L. mas.n. Azotobacter 

 nitrogen rod. 



Description same as for the family. 



The type species is Azotobacter chroococcum Beijerinck. 



1. Azotobacter chroococcum Beijer- 

 inck, 1901. (Cent. f. Bakt., II Abt., 7, 1901, 

 567; also see ibid., 9, 1902, 3.) 



chro.o.coc'cum. Gr. noun chroa color, 

 complexion; Gr. noun coccus a grain; M.L. 

 neut.n. chroococcum colored coccus. 



Rods, 2.0 to 3.0 by 3.0 to 6.0 microns, 

 occurring in pairs and packets and occasion- 

 allj^ in chains. The cells show three or four 

 refractile granules. The organisms are sur- 

 rounded by a slimy membrane of variable 

 thickness, usually becoming brownish in 

 older cultures, due possibly to the con- 

 version of tyrosine to melanin. The coloring 

 matter is insoluble in water, alcohol, ether 

 or chloroform. Motile bj' means of numerous 

 peritrichous flagella (Hofer, Jour. Bact., 

 47, 1944, 415). Gram-negative. 



Grows in absence of organic nitrogen. 



Gelatin colonies: Very small, circular, 

 yellow, granular, later becoming yellowish 

 brown. 



Gelatin stab: Onlj' slight growth in the 

 stab. No liquefaction. 



Mannitol agar stab: Gray, may become 

 brownish. 



Nutrient broth: No growth even in the 



presence of glucose; peptone utilized with 

 difficult}'. 



Litmus milk: Becoming clearer in 10 to 

 14 days. 



Potato: Glossy, barely visible, slimy to 

 wrinkled; may become yellowish, brownish 

 .yellow or chocolate-brown. 



The organism fixes atmospheric nitrogen 

 and gives off CO2, utilizing glucose and 

 sucrose. Other generally used carbon com- 

 pounds are fructose, maltose, mannitol, 

 inulin, dextrin, galactose, arabinose, starch, 

 glycerol, ethyl alcohol, acetate, butyrate, 

 citrate, lactate, malate, propionate and 

 succinate. 



Nitrate : Improves growth in amounts 

 less than 1 gm per liter; greater amounts 

 are toxic. 



Fixes nitrogen moderately actively. 



Chemical analysis: Four-day cultures 

 grown upon mannitol agar, when dried, are 

 found to contain less than 0.5 per cent of 

 hemicelluloses, less than 20 per cent of crude 

 protein, less than 5 per cent of ash, and 

 more than 30 per cent of lignin-like mate- 

 rials (Greene, Soil Sci., 39, 1935, 327). The 

 nitrogen fraction contains less than 1 per 



* Revised by Dr. A. W. Hofer, New York State Experiment Station, Cornell University, 

 Geneva, New York, Jime, 1938; further revision by Dr. A. W. Hofer, May, 1954. 



