ter're.gens. L. noun terra soil; L. part. adj. egens requiring; M.L. part. adj. terregens soil-requiring. Rods, 0.6 to 0.8 by 1.0 to 5.0 microns, usu- all}^ occurring in V-shaped pairs as a result of snapping division. The cells vary in shape from short, straight rods to irregular, curved or swollen forms; some of the longer rods show rudimentary budding. In older cul- tures (usually after 3 days), coccoid cells, formed by the fragmentation of long rods, predominate. The cocci vary in size accord- ing to the medium: on soil extract agar the cells measure 0.6 to 0.7 micron, and on richer media containing yeast extract, they are 0.8 to 0.9 micron in diameter. When freshl}^ transferred, the larger coccoids (cystites) may germinate rod forms, up to three in number. Gram-negative; the coc- coid cells are Gram-variable, usually Gram- negative. Requires a growth factor, 'terregens fac- tor' (TF), present in soil extract or in cul- ture filtrates of Arthrobacter pascens. No growth in standard media; these may be rendered suitable for growth by addition of soil extract or culture filtrate of A . pascens. Gelatin stab: Yellowish growth, best at surface; no liquefaction. Agar colonies: Circular, 1.0 to 2.5 mm in diameter, entire, convex, yellowish brown, glistening. Agar slant: Growth filiform, flat, pale brown, glistening. Soil extract agar slant: Growth filiform, flat, yellowish brown, glistening, soft; sur- face finely roughened. Broth: Moderately turbid; no surface growth; stringy, yellowish sediment. Potato: Slight or no growth. Milk: No change after 6 weeks. Indole not produced. Hydrogen sulfide not produced. Slight acid from glucose and sucrose; trace or no acid from other sugars; no gas produced. Acetylmethylcarbinol not produced. Starch not hydrolyzed. Nitrites produced from nitrates. Urease not produced. Unable to utilize nitrates or ammonium salts as nitrogen source, or citrates as sole carbon source, even in presence of growth factor. Catalase-positive. Aerobic. Optimum temperature, between 20° and 26° C.; grows from 15° to 35° C.; no growth at 10° or 37° C. Source: Isolated from soil. Habitat: Soil.
