Aerial mycelium: None. Spherical conidia produced on branching, short conidio- phores. Conidia blue. Liquid media: Growth at bottom forms firm, round, white to pink granules. Gelatin: Rapid liquefaction. Milk: May be coagulated, but digestion very slight. Sucrose not inverted. Starch is hydrolyzed. Cellulose not decomposed. Nitrites not produced from nitrates. Aerobic. Source: Isolated from soil. Habitat: Occurs infrequently in soil. Germs III. Thermoactinomyces Tsiklinsky, 1899. (Ann. Inst. Past., 13, 1899, 501; also see ibid., 17, 1903, 206.) Ther.mo.ac.ti.no.my'ces. Gr. noun thermus heat; Gr. noun actis, actinis a ray; Gr. noun myces fungus; M.L. mas.n. Thermoactinomyces heat (-loving) ray fungus. The genus Thermoactinomyces is, in some respects, similar to Micromonospora, especially in its ability to produce single conidia at the tips of simple or branching conidiophores, which may be so short that they often appear to be produced directly on the mycelium. In other respects, notably in appearance and in ability to produce a true aerial mycelium, this genus resembles Streptomyces. It comprises, so far, only forms capable of growing between 50° and 65° C. Some have their optimum temperature at 60° C. Three species have been recognized so far. The type species is Thermoactinomyces vulgaris Tsiklinsky. Key to the species of genus Thermoactinomyces. I. Aerial mycelium white. A. No soluble pigment produced. 1. Thermoactinomyces vulgaris. B. Soluble wine-colored to rose pigment produced in certain media. 2. Thermoactinomyces thalpophilus . II. Aerial mycelium grayish green. 3. Thermoactinomyces monosporus. 1. Thermoactinomyces vulgaris Tsik- linsky, 1899. (Thermophile Cladothrix, Ked- zior. Arch. f. Hyg., 27, 1896, 328; Tsiklinsky, Ann. Inst. Past., 13, 1899, 501; Micromono- spora vulgaris Waksman, Umbreit and Gor- don, Soil Sci., 47, 1939, 51.) vul.ga'ris. L. adj. vulgaris common. Vegetative growth: Grows well on organic and synthetic media. Mycelium 0.5 micron in diameter. No soluble pigment. Aerial mycelium: White, powdery. Spher- ical and ellipsoidal spores are borne singly at the end of short branches from which they are easily broken. Gelatin: Liquefaction. Agar: Grows well, produces aerial my- celium. Synthetic agar: Colorless growth, covered with white aerial mycelium. Sporophores very short, not exceeding 2 microns in length, often only 0.5 to 1.0 micron. Spores ellipsoidal or spherical, often appear to sit directly on mycelium. Broth: Growth in form of white pellicle and often as compact balls on bottom of culture. Milk: Coagulated and peptonized. Potato: Grows well. Sucrose not inverted. Starch is hydrolyzed. Cellulose not decomposed. Optimum temperature, 57° C. Grows be- tween 48° and 68° C. Source: Isolated from compost. Habitat: Found in human and animal excreta, high-temperature composts, self- heated hay and soil. 2. Thermoactinomyces thalpophilus Waksman and Corke, 1953. (Jour. Bact., 66, 1953, 377.) thai . po'phi . lus. Gr. noun thalpus warmth,
