Rods, 0.5 to 1.0 by 1.0 to 4.0 microns, which may be curved or club-shaped; oc- casionally rudimentary filamentous forms maj' occur, although branching is infre- quent. The longer forms fragment into short rods and cocci. Cells in older cultures are almost exclusively coccoid and vary from 1.0 to 3.0 microns in diameter. When trans- ferred to fresh media, the larger coccoid cells (cystites) germinate, giving rise to one or two rod-shaped cells (Sguros, Jour. Bact., 69, 1955, 28). Non-motile. Gram-negative; the cystites are Gram-negative and usually possess a Gram-positive granule. Gelatin stab: Slow, crateriform liquefac- tion. Agar colonies: Punctiform or circular, convex, opaque, smooth, glistening; viscid or butj'rous varieties may occur. Agar slant: Growth abundant, filiform, opaque, smooth, glistening; yellow and pearl-gray strains occur, the former being viscid and the latter butyrous in consist- ency. Asparagine agar: Growth filiform, opaque, smooth, glistening; development of chromo- genesis retarded. Nicotine agar: Abundant growth with the production of a diffusible, deep blue pigment which turns reddish to yellowish brown with age. Broth: Abundant growth; surface ring; viscid sediment. Potato: Abundant growth, yellow to gray varying with the strain. Milk: Slow peptonization and reduction of litmus; reaction alkaline. Indole not produced. Hydrogen sulfide not produced. Acid but no gas from fructose and su- crose; acid in glucose broth weak and tran- sient; with other carbohydrates, reaction alkaline. Acetylmethylcarbinol not produced. Starch is hydrolyzed. Nitrites produced from nitrates. Utilizes nitrates and ammonium salts as nitrogen sources; citrates utilized as sole source of carbon. Catalase-positive. Aerobic. Optimum temperature, 25° C. Comment: Yellow-viscid and pearl -white- butyrous biotypes of this species have been recognized (Sguros, loc. cit.). Source: Isolated from tobacco leaves. Habitat: Probably soil. 5. Arthrobacter aurescens (Clark, 1951) Phillips, 1953. (Arthrobacter globifonne var. aurescens Clark, Proc. Soil Sci. Soc. Amer., 15, 1951, 180; Phillips, Iowa State Coll. Jour. Sci., 27, 1953, 240.) au.res'cens. L. v. auresco to become golden; L. part. adj. aurescens becoming golden. Rods which vary in shape and size accord- ing to the nature of the culture medium: 0.5 by 1.0 to 3.0 microns on plain agar and 0.6 to 0.8 by 1.0 to 6.0 microns on enriched solid media; the cells may be straight, curved or swollen or may show rudimentary branching, especially in enriched liquid media. In older cultures the cells become coccoid, measuring 0.6 micron in diameter. Non-motile. Gram-variable; the cocci are generally Gram-negative although the larger coccoids (cystites) are usually Gram- positive. Gelatin stab: Stratiform liquefaction; yellowish surface growth; moderate sedi- ment; liquid very turbid. Agar colonies: Circular, up to 2 mm in diameter, convex, yellow, opaque, smooth, glistening. Agar slant: Growth abundant, filiform, opaque, smooth, creamy lemon-yellow, soft, waxy luster with a metallic sheen. Soil-extract agar slant: Growth filiform, smooth, cream-colored becoming pale yel- low, glistening, soft. Asparagine agar slant: Growth filiform, lemon-yellow, soft, waxy luster; surface uneven; edge finely indented. Nicotine agar: Growth slow and sparse, flat, translucent, colorless. Broth: Moderately turbid; no surface growth; considerable cream-colored sedi- ment. Potato: Growth moderate, brownish yel- low, dull, cheesy in consistency. Milk : Pale yellow surface and ring growth ; clearing (3 to 4 daj's) without coagulation; cream-colored sediment. Indole not produced.
