Page:Bergey's manual of determinative bacteriology.djvu/305



A.zo.to.bac.te.ra'ce.ae. M.L. mas.n. Azotobacter type genus of the family; -aceae ending 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 carbohydrate or other energy source. Grow best on media deficient in nitrogen. Soil and water bacteria.

There is a single genus.

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