128 



THE ACTINOMYCETES, Vol. II 





'«V 



Figure 31. Variation in morphology of spore-bearing hyphae in *S'. aureofaciens: (left) natural vari- 

 ant A 377; (center) natural variant AB 374; (right) induced mutant A 377-2G55 (Reproduced from: 

 Backus, E. J. et al. Ann. N. Y. Acad. Sci. 60: 101, 1954). 



that the whole series be designated as Flavus- 

 parrus. Considerable variation was found 

 among the members of this series. 



Morphological Characters 



Hyphae: (a) short, gnarled, and in clus- 

 ters, with short oval spores; or (b) long, 

 straight with spherical spores; or (c) long 

 with long corkscrew spirals and spherical 

 spores (Fig. 31). 



I'hysiological Characters 



Sucrose nitrate agar: Growth cream- col- 

 ored, yellow to brownish to orange; reverse 

 yellow to orange. Aerial mycelium cream- 

 colored, straw-colored to citron-yellow, 

 straw-yellow, grayish-yellow to bluish-gray 

 to white, or absent. Soluble pigment light 

 yellow to brownish. 



Glucose-asparagine agar: White to cream- 

 colored growth, sometimes turning orange. 

 Aerial mycelium white to gray. Soluble pig- 

 ment none, or brownish to yellow. 



Nutrient agar: Growth cream-colored to 

 yellowish to brownish. Aerial mycelium 

 white, cream-colored to gray, or absent. 

 Soluble pigment yellow to almost none. 



Gelatin: Cream-colored to yellow to 



orange-yellow ring on surface. Aerial myce- 

 lium cream-colored, straw-green to gray, or 

 absent. Soluble pigment brownish to yellow, 

 or absent. Liquefaction varies from slow to 

 rapid. 



Potato: Growth abundant, lichenoid, 

 cream-colored to brownish to orange. Aerial 

 mycelium white, cream-colored, gray to 

 yellow. Usually no soluble pigment; occa- 

 sional yellowish-orange pigment. 



Milk: Surface growth abundant or thin 

 gray to black ring. Aerial mycelium white to 

 gray or absent. Milk not coagulated but 

 peptonized, the rapidity depending on ex- 

 tent of growth. 



Antagonistic properties: Some members of 

 the group produce highly important anti- 

 biotics, such as the tetracyclines, that have 

 found extensive application in chemotherapy 

 and in food preservation (Kochi et al. ,1952). 



A careful study of the literature reveals 

 the fact that a large number of species found 

 in nature belong to this series. Some of them 

 have been well recognized and described. 

 Various others may be added, but many 

 have been only insufficiently described. On 

 the basis of the recognized information, the 

 S. flavus series may be said to include the 



