THERMOPHILIC ACTINOMYCETES 



307 



it is distinct from it, however, in the forma- 

 tion of a typical aerial mycelium. 



Henssen emended this genus as follows: 

 Colonics on agar colorless or yellow to 

 orange. Substrate mycelium no1 septated. 

 Aerial mycelium not sharply delimited; 

 white or bluish-green. Aerial hyphae are 

 simple or branched, formed as terminal or 

 side branches; they may also be curved; 

 they grow upwards from the substrate my- 

 celium. Spores, single or in chains, remain 

 on the unbranched aerial hyphae. The or- 

 ganisms are thermophilic, capable of grow- 

 ing at 50-65°C. They are aerobic or faculta- 

 tively aerobic. Some have their optimum at 

 60°C. 



Type species: Thermoactinomyces thalpo- 

 philus Waksman and Corke. 



The genus can be classified as follows: 



1 . Aerial mycelium unite. 

 a. No soluble pigment . 



is. Thermoactinomyces vulgaris 

 1). Soluble wine-colored to rose pigment in 

 certain media. 



3. Thermoactinomyct s thalpophilus 

 II. Aerial mycelium grayish-green. 



2. Tin rmoactinomyces monosporus 

 III. Aerial mycelium scant . white to bluish-green. 



a. No soluble pigment. 



1. Thermoactinomyces glaucus 



b. Soluble pigment green. 



5. Thermoactinomyces viridis 

 L\". Aet'ial mycelium white to dark gray. 



4. Thermoactinomyces thei mophilus 



1. Thermoactinomyces glaucus Henssen, 

 l ( .).->7 (Henssen, A. Arch. Mikrobiol. 26: 

 157:5-414, 1957). 



Morphology: Spore chains simple or 

 branched, about 7 ^ long, containing 4 to 

 10 spores. The chains are straight or bent. 

 Spores round or oval, 0.9 to 1.4 by 0.5 to 

 L.9/Z- 



Cultural properties: Growth almost color- 

 less; aerial mycelium white to bluish-green. 

 Facultative aerobe. 



Sucrose nitrate agar: Growth moderate. 

 Aerial mycelium moderate. 



Glycerol-asparagine agar: Growth moder- 

 ate. Aerial mycelium scant. 



Nutrient agar: Growth sparse. 



Cellulose-dextrin agar: Growth good. 

 Aerial mycelium abundant, white to green. 

 Cellulose decomposed very actively. 



Gelatin: Unchanged. 



Potato: Individual colonies without aerial 

 mycelium. 



Standi: Slow hydrolysis. 



Nitrate reduction: Positive. 



.Milk: Slowly coagulated and peptonized. 



Habitat: Composted sheep manure. 



2. Thermoactinomyces monosporus (Leh- 

 mann and Schiitze) Waksman (Schiitze, H. 

 Arch. Hyg. 67: 35, 1008; after Krassilnikov, 

 1<)41). 



Morphology: Substrate hyphae about 1.0 

 /x in diameter. Oval spores 1.5 to 1.8 by 

 1.0 to 1.4 /j. produced singly. 



Agar media: Growth yellowish, compact, 

 smooth or lichenoid. Aerial mycelium gray- 

 ish-green. Good sporulation of hay infusion- 

 peptone agar; somewhat less on glycerol- 

 peptone and lactose-peptone agar; none on 

 peptone-glucose agar. 



Potato: No growth. 



Gelatin: Liquefaction positive. 



Milk: No coagulation or peptonization. 



Blood serum: Good, smooth growth: lique- 

 faction positive. 



Temperature: Optimum 37-55°C; grows 

 poorly at 27°C and not at all at 60°C. 



Habitat: Self-heated hay. 



Remarks: Henssen (1957) considers this 

 species as more closely related to the genus 

 Thermomonospora. 



:!. Thermoactinomyces thalpophilus Waks- 

 man and Corke, 1'.).").'; (Waksman, S. A. and 

 Corke, C. .1. Bacteriol. 66: :',77, 1953). 



Morphology: Spores, produced singly or 

 in short chains, are round, 0.S to 1.2 fi. 



Agar media: Grows equally well on a 

 variety of media under aerobic and anaero- 

 bic conditions. Colonies colorless to orange. 



