CLASSIFICATION OF THE ACTINOMYCETES 25 



albido-flavus. Numerous other cultures belonging to this group have been 

 isolated from soil and other natural substrates by Krainsky, by Waksman 

 and Curtis, and by others. 



This group is characterized by cream-colored to yellow to golden yellow 

 growth on most media. The aerial mycelium is white to gray to mouse-gray. 

 The sporophores are long, spiral-shaped; the spores are spherical, usually 

 0.7 ix in diameter. No brown pigment is produced on protein media. A 

 yellowish green to golden pigment is often formed in synthetic and com- 

 plex organic media. The cultures are strongly proteolytic and diastatic; 

 sucrose is inverted, nitrate is reduced. Many of the strains are strongly 

 antagonistic and are able to produce active antibiotics, some of which have 

 found extensive application as chemotherapeutic agents. 



The following species have been recognized and described in the litera- 

 ture. Various others have been listed but only insufficiently described. The 

 recognized species can be classified as follows : 

 A. Do not excrete any soluble pigment into medium. 

 I. Colonies lemon-yellow to golden yellow, 

 a. Aerial mycelium not well developed. 



a. Proteolytic activity strong. 



Streptomyces citreus 



b. Proteolytic activity weak. 



Streptomyces alboflavus 

 2. Aerial mycelium well developed. 



Streptomyces flavus 

 II. Colonies yellowish brown to bright yellow. 



1. Colonies bright yellow, golden. 



a. Proteolytic activity strong. 



Streptomyces sulfureus 



b. Proteolytic activity weak. 



Streptomyces aureus 

 S. antibioticus and S. tanashiensis probably also belong to this 

 group. 



2. Colonies yellow-brown. 



a. Cultures do not excrete any brown substances into medium. 

 a 1 . Cultures decompose cellulose. 



Streptomyces cellulosae 

 b 1 . Cultures do not decompose cellulose. 

 Streptomyces graminearis 



b. Cultures excrete brown substance into medium. 

 a 1 . Aerial mycelium green. 



a 2 . Thermophilic forms. 



a 3 . Aerial mycelium dark gray or green. 

 Streptomyces thermophilus 



