cent of amide nitrogen, less than 1 per cent of humin nitrogen and about 1 per cent of basic nitrogen. Aerobic. Optimum temperature, between 25° and 28° C. Distinctive characters: Inability to grow in peptone media, even in the presence of glucose; frequent occurrence of a dark brown or black pigment. Source: Isolated from soil. Habitat : Occurs naturally in the majority of neutral or alkaline field soils. 2. Azotobacter agilis Beijerinck, 1901. (Cent. f. Bakt., II Abt., 7, 1901, 577.) a'gi.lis. L. adj. agilis quick, agile. Rods, 4 to 6 microns in length, almost spherical. Actively motile by means of numerous, peritrichous flagella (Hofer, Jour. Bact., 47, 1944, 415). Some strains are reported to be non-motile. Gram-nega- tive. Grows in absence of organic nitrogen. Gelatin: No liquefaction. Mannitol agar colonies: Circular, gray- ish white, translucent with whitish center. Washed agar colonies : Show slight bluish green fluorescence. The presence of a fluo- rescent pigment is readily demonstrated by placing cultures under ultraviolet light, 3600 A. Examination by paper chromotog- raphy indicates that this pigment is not fluorescin, the pigment found in fluorescent pseudomonads (Johnstone, Jour. Bact., 69, 1955, 481). Mannitol agar slant: Grayish, translu- cent, fluorescent. Plain agar slant : Yellowish white, smooth, glistening, translucent with opaque center. Broth: Turbid, with sediment. Litmus milk: Becoming clear in 10 to 14 days. Potato: Yellowish white, slimy, becom- ing yellowish brown. In the presence of organic acids, a green- ish or reddish pigment is formed. The organism fixes atmospheric nitrogen actively and gives off CO2 . Aerobic. Chemical analysis: Four-day cultures grown upon mannitol agar, when dried, con- tain more than 4 per cent of hemicelluloses, more than 45 per cent of crude protein, more than 7 per cent of ash, and less than 4 per cent of lignin-Iike materials. The nitrogen fraction contains more than 1 per cent amide nitrogen, more than 1 per cent humin nitrogen, and 2 per cent or more of basic nitrogen (Greene, Soil Sci., 39, 1935, 327). Optimum temperature, between 25° and 28° C. Distinctive characters: Lack of a brown pigment; occasional fluorescence; growth in peptone broth containing glucose. Comment: A non-chromogenic variety of this species has been recognized by Kluyver and van den Bout (Arch. f. Mi- krobiol., 7, 1936,263). Source: Originally isolated from canal water at Delft. Habitat: Occurs in water and soil. 3. Azolobacter indicus Starkey and De, 1939. {Azotobacter iniicum (sic) Starkey and De, Soil Sci., 47, 1939, 337.) in'di.cum. L. adj. indicus of India. Ellipsoidal rods, 0.5 to 1.2 by 1 7 to 2.7 microns when grown on nitrogen-free glu- cose agar. One of the distinctive character- istics is the presence of two large, round, highly refractive bodies in the cells, one usually at each end. Motile by means of numerous peritrichous flagella (Hofer, Jour. Bact., 47, 1944, 415). Gram-negative. The organism grows slowly but in time produces large amounts of slime. Has high acid tolerance, since it grows from pH 3 to 9. Sucrose or glucose agar plates: Colonies are colorless, round, very much raised and uniformly turbid, having much the appear- ance of heavy starch paste. After two weeks, a buff to light brown color develops. Mannitol agar slant: Grows very poorly. Peptone agar slant with 0.5 per cent glu- cose: Limited grayish growth. Nutrient broth: No growth. Liquid media: Generallj^ turbid with some sediment. Fixes atmospheric nitrogen readily with either glucose or sucrose as source of energy. Aerobic. Optimum temperature, 30° C.
