Waksman — 72 — Actinomycetes 



mycin-producing strains of S. griseus into inactive strains free from 

 aerial mvcelium (395); (e) change of strain of S. griseus from a color- 

 less ^'egetative culture to a pink variant, accompanied by a change in 

 antibiotic-producing capacity. 



Early students of the actinomycetes (388) observed that the acid-fast 

 organism which causes infection in man gives rise to two subtypes, one 

 simple in nature and liquefying gelatin, and the other producing pseu- 

 dotubercles and not liquefying gelatin. The second form was looked 

 upon as intermediary between actinomycosis and tuberculosis. 



Numerous references are found in the literature (188) to the trans- 

 formation of actinomycetes, under special conditions of culture, into 

 mycobacterium-like organisms, or into diphtheroid organisms, and vice 

 versa. Of special interest are the transformations of anaerobic, short- 

 hyphaed forms of actinomycetes into aerobic, long-hyphaed forms. Dis- 

 sociation of pathogenic actinomycetes into aerobic and anaerobic strains 

 has frequently been reported (427). It has also been reported (319) 

 that two sorts of anaerobic colonies were isolated from the pus of actino- 

 mycosis, one smooth and composed of gram-negative rods, and the other 

 adherent and composed of gram-positive filaments. These were looked 

 upon as S and R forms of the organism; even a transitional O form was 

 recognized. These variations have often been considered as a part of 

 the life cycle of the organisms. The composition of the medium, that 

 is, whether complex organic or simple inorganic, protein-rich or carbo- 

 hydrate-rich, and its reaction greatly influence the stability of the cul- 

 ture, or the cycle of growth of actinomycetes. This is true also of 

 environmental factors, especially moisture content, aeration, and tem- 

 perature. The presence of other organisms, resulting in antagonistic 

 and associative eff^ects, likewise influences the variation of the culture. 



Individual variations and group variations may also be distinguished. 

 The size of mycelium fragments, the formation of grains in the disinte- 

 gration of the cells, the formation of conidia and chlamydospores— all 

 influence the cycle of growth of the individual organism, with the re- 

 sulting variations and modifications. 



The problem of cell polymorphism among actinomycetes has also 

 aroused much attention. This property must be taken into considera- 

 tion in placing any organism in its taxonomic position (191). The 

 formation of new races or strains can be accounted for on the basis of 

 changes, which are expressed by the surface appearance of the colony, 

 whether smooth or rough, by the presence or absence of aerial myce- 

 lium, by the manner of sporulation, by changes in pigmentation, and 

 by other cultural characteristics. 



Mutations.— The formation of saltants or mutants by actinomycetes 

 must be regarded as in a class by itself, distinct from the variants. The 

 mutations may be said to include the following types: formation of 

 white strains from blue forms; formation of strains free from aerial mv- 

 celium from strains producing such mycelium or vice versa; formation 



