Chapter IV — 71 — Variations and Mutations 



mycelium may be lost. The size, shape, and color of colonies, the 

 length and abundance of mycelium, and the manner of spore formation 

 are influenced by the composition of the medium and the age of the 

 culture. 



In more recent studies (199) the general variations among the 

 actinomycetes have been divided into three classes: (a) adaptive, or 

 amenable to environment; (1?) continuous or fluctuating, as shown by 

 diff^erences in the colonies plated out from the same culture; (c) devel- 

 opmental, resulting in saltations or mutations. The adaptive type is 

 usually characterized by a decrease in the size of the colony, a loss of 

 the capacity to form sporogenous hyphae, a reduction of the ability 

 to utilize certain nutrients, a change in pigment production, and a loss 

 in the capacity to produce antibiotic substances. The continuous type 

 is most clearly marked by the nature and intensity of the pigment pro- 

 duced by the organism, as well as by the capacity to produce a given 

 antibiotic. The developmental variations are expressed in the pres- 

 ence or absence of aerial mycelium, pigmentation of the vegetative or 

 aerial mycelium, and production of antibiotics. Some of these changes 

 can be reversed to the original by growing the organism on special me- 

 dia, such as glycerol nutrient agar, or in some natural medium, such as 

 sterile soil. Other variations or mutations are more permanent or stable 

 in nature, although only on rare occasions. 



In spite of these many types of variations, the constancy of strains 

 or species of actinomycetes can be maintained if proper care is taken in 

 growing the cultures on suitable media. The recognition of this fact 

 has led some investigators (98, 318) to emphasize the constancy of the 

 characters of actinomycetes, as contrasted to others who denied such 

 constancy. 



Tempel (414) observed that several actinomyces strains failed to 

 show, under constant conditions of culture, any sudden changes either 

 in morphology or in physiology, which could be considered as muta- 

 tions. The physiological changes due to the effects of temperature, 

 aeration, reaction and composition of medium w^ere confirmed, but these 

 changes were not permanent in nature. Rippel and Witter (361) 

 could not obtain any variabilit)^ among several actinomycetes, either 

 by changing cultural conditions or by irradiation by means of Rontgen 

 rays or ultraviolet rays. Spontaneously occurring sectors gave normal 

 cultures on transfer. 



Hereditary variations.—Several specific forms of hereditary variation 

 among actinomycetes have received particular consideration. It is suf- 

 ficient to mention the following: (a) transformation of an actinomyces 

 into a mycobacterium-like organism (328, 378), the former being re- 

 generated by cultivation on certain media, such as potato; (I;) trans- 

 formation of an actinomyces into diphtheroid organisms (211); (c) 

 transformation of anaerobic, short hyphal-producing forms into aerobic, 

 long hyphal forms (328); (t?) change of aerial mycelium and strepto- 



