Waksman — 78 — Actinomycetes 



shaken cultures was compared with that of the original culture, the first 

 variant of the first strain was almost completely inactive, whereas the 

 second variant of that strain was more active than the parent strain, and 

 the strains free of aerial mycelium were completely inactive. 



The production of streptothricin by S. lavendulae was thus associ- 

 ated with the ability of the culture to form aerial mycelium, similar to 

 one of the variants of S. griseus. In both cases, the variants which 

 failed to produce aerial mycelium likewise produced culture filtrates 

 which possessed no antibiotic potency. Aerial mycelium is not, of 

 course, a determinant for the formation of antibiotics, since numerous 

 cultures of both S. griseus and S. lavendulae which produce abundant 

 aerial mycelium are unable to form the respective antibiotics. 



Jones (201) examined 1,298 freshly isolated cultures of Strepto- 

 myces. About 20 per cent of these showed from the start considerable 

 fluctuation in the production of aerial mycelium, 6 per cent producing 

 only vegetative growth in the first transfer. The question was, there- 

 fore, raised: How many representatives of the fluctuating group may 

 be assigned to the genus Streptomyces or Nocardia? 



Culture Constancy:— In the utilization of actinomycetes for the 

 production of antibiotics, it is highly important to be able to depend 

 upon the constant characters of a culture. In view of the fact that a 

 given organism may be subject to a great many variations due to con- 

 ditions of cultivation and environment, as well as to other conditions, it 

 is essential to be able to come back to the original culture. 



With the purpose in view, a given culture is usually inoculated into 

 moist sterile soil. After the culture has made some growth, the soil is 

 allowed to dry out. The culture can thus be kept for a considerable 

 time. When required, the soil is plated out and the culture reisolated 

 (200). 



On comparing cultures kept in soil with similar cultures kept in 

 synthetic media, it was found that the latter tended to lose their capacity 

 for producing aerial mycelium and for abundant sporulation (115). 



