Chapter IV — 75 — Variations and Mutations 



the designation of such groups as alhus, flavus, and violaceiis. Waks- 

 MAN also proposed a key for the separation of species of actinomycetes on 

 the basis of the pigment produced on organic and synthetic media, in- 

 cluding soluble and insoluble (or exo- and endo-) pigments. 



More detailed study has revealed, however, that on continued culti- 

 vation of organisms, the pigment undergoes changes in its nature, or it 

 disappears altogether. Thus an organism designated as A. verne, be- 

 cause of the soluble green pigment produced in the medium, lost that 

 property on continued cultivation. When the characters of an organism 

 are based on pigmentation, it becomes very difficult to make comparisons 

 even if type cultures are available. Thus, one of the most widely used 

 cultures of actinomycetes, the streptomycin-producing strain of S. 

 griseiis, can hardly be recognized either by comparison with the original 

 cultures of Waksman and Curtis or from the original description of 

 Krainsky, since the type culture lost its characteristic pigmentation and 

 Krainsky's description did not quite correspond with the published 

 description of its pigmentation. 



Among the other cultural variations reported for actinomycetes, the 

 lytic activities of many of the strains deserve consideration, as pointed 

 out previously (p. 60). The phenomenon of Ivsis, whether considered 

 as a part of the life cycle of the organisms or looked upon as stages of de- 

 generation of a culture, has a bearing upon the production of new types. 

 This holds true also for the effect of phage upon the del^elopment of 

 resistant strains. 



Marked variations in agar-decomposition and pigmentation of S. 

 coeJicoIor have also been observed (408). Erikson (115a) found that 

 the major variations of S. coelicoJor comprise loss of pigmentation, loss 

 of aerial mycelium, and occasionally also loss of agar-liquefaction. Sin- 

 gle spore isolations from aerial mycelium brought out the possibility of 

 inherent differences in the sister spores of the same chain. Spontaneous 

 occurrence of variants may be found more readily in the spores of de- 

 generate colonies, rendered atypical by artificial methods of cultivation, 

 than in the spores of the aerial mycelium of typical colonies. In an 

 agar-liquefying strain, 3 out of 15 spores lost the power to produce 

 the pigrhent and to liquefy agar. A non-agar-liquefying strain, which 

 had lost the power of pigmentation, gave a variant which produced 

 sectored colonies, some of which possessed the blue pigment. 



Physiological and applied variations.— These can best be described 

 by an analysis of the variation of two important economic groups of 

 actinomycetes, namely, those that cause potato scab and those that pro- 

 duce antibiotics. These physiological variations are usually more quan- 

 titative than qualitative in nature. 



Potatoes show considerable variation in their resistance to scab. 

 This has been ascribed either to differences in the environment in which 

 the potatoes are growing or to physiological differences of the strains of 

 S. scabies, the causative agent of infection. 



