100 



THE ACTINOMYCETES, Vol. I 



strains into inactive strains that may also 

 be free from aerial mycelium; (e) change of 

 colorless strains into pink variants, accom- 

 panied by a change in the nature of the 

 antibiotic-producing capacity; (f) develop- 

 ment, among acid-fast organisms which 

 cause infection in animals, of two subtypes, 

 one licjuefying gelatin and the other not 

 liquefying gelatin. 



Dissociation of pathogenic actinomycetes 

 into aerobic and anaerobic strains has fre- 

 cjuently been recorded. Two types of anaero- 

 bic colonies have been isolated from the pus 

 of actinomycosis, one smooth and composed 

 of gram-negative rods, and the other ad- 

 herent and composed of gram-positive fila- 

 ments; these were looked upon as S and R 

 forms. These variations have often been 

 considered as a part of the life cycle of the 

 organisms. 



The causes of variation among bacteria in 

 general and actinomycetes in particular 

 may be briefly summarized as follows: 



1 . Nature of substrate in which the organ- 

 ism is growing, such as soil versus artificial 

 media, solid versus liquid media. 



2. Nature of the nutrients, including 

 synthetic versiis organic media, simple versus 

 complex media, dilute versus concentrated 

 (salt) media. 



3. Environmental factors of growth, nota- 

 bly temperature, moisture content, aera- 

 tion, and reaction. 



4. Inoculinn, whether vegetative or spore 

 material, whether a heavy mass inoculum 

 or single-cell preparations. 



5. Age of culture, whether continuous or 

 fretiuently transferred. 



6. Presence of other organisms that may 

 exert antagonistic; or associative efl'ccts. 



7. Presence of antimicrobial agents, giving 

 rise to the concept of directed variations. 



8. Lytic phenomena, including phage 

 effects. 



9. Host specificity, in pathogens. 



The nature of the variations may be 



morphological, comprising colony structure 

 and cell structure, or biochemical, com- 

 prising formation, both (juantitative and 

 qualitative, of important metabolic products 



Kriss recognized four types of variation: 

 morphological, cultiu'al, physiological, and 

 applied. These are illustrated by the varia- 

 bility of a culture of S. coelicolor, as presented 

 in Table IG. 



Duggar et al. made a detailed study of the 

 morphological and physiological variability 

 of certain antibiotic-producing organisms 

 belonging to the genus Streptomyces. They 

 concluded that these variations proceed in 

 nature as well as in culture, along parallel 

 lines. They were inclined to accept the 

 modern tendency to propose a new name and 

 description for a recently isolated culture 

 rather than go through the existing hazard 

 of "identification," because of the inadequate 

 study of the strains and lack of "com- 

 prehensiveness" of published specific de- 

 scriptions. Although they agreed on the un- 

 soundness of reducing the species concept 

 to "racial or near-biotype rank," they were 

 willing to consider as a basis of species 

 differentiation "minor or single variations of 

 morphological or developmental features, of 

 responses to environmental changes, of 

 differential election of nutrients or of meta- 

 bolic differences." 



On examining 1,298 freshly isolated cul- 

 tures of streptomyces, Jones found that 

 about 20 per cent showed considerable fluc- 

 tuation in the production of aerial mycelium, 

 and () per cent formed only substrate growth 

 in the first transfer. In a detailed study of 

 the variations of five strains, Jones concluded 

 that although ^•ariations were ninnerous, 

 they were mostly temporary. Saltations 

 (mutations) were the only permanent varia- 

 tions. 



Further studies on the variability of anti- 

 biotic-producing strains of species of Strepto- 

 myces ha\'e been made by Frommer, Backus 



