20 ACTINOMYCETES 



b. Pigment faint brown. 



143. Streptomyces kimberi 



2. Growth on potato plug abundant, becoming black; aerial myce- 

 lium white-gray; plug discolored. 



144. Streptomyces somaliensis 



3. Growth on some media pink-colored. 



145. Streptomyces panjae 



4. Aerial mycelium on most media profuse, white; spiral formation. 



146. Streptomyces willmorei 

 E. No aerial mycelium. 



147. Streptomyces sterilis group 



This group comprises forms that have lost the capacity to produce aerial 

 mycelium. They can be subdivided into Streptomyces sterilis albus, Strep- 

 tomyces sterilis ruber, Streptomyces sterilis viridis, Streptomyces sterilis flavus, 

 etc. 



Classification of Certain Important Group-Species of 



Streptomyces, from Point of View of Antibiotic 



Production 



Careful examination of the foregoing systems of classification of species 

 of Streptomyces will reveal considerable overlapping of species. Frequently 

 a given culture may be placed in one species or another, depending on the 

 particular media and on the conditions used for growing the organism and 

 the idiosyncrasies of the observer. Classification becomes particularly diffi- 

 cult when one bears in mind the marked variation frequently observed 

 between different isolates of the same species and the tendency of individual 

 cultures to mutate upon continued cultivation in artificial media. The fact 

 that identifications are usually based upon comparisons with published 

 descriptions rather than with type cultures has resulted in the tendency to 

 create new species on the basis of minor differences. 



These considerations have often led to emphasis upon group characteriza- 

 tion rather than upon single culture-species. Several such groups, especially 

 those comprising the more important antibiotic-yielding strains, may be 

 selected for further examination. The individual species or strains within 

 each of these groups vary greatly in their cultural and morphological proper- 

 ties, as well as in nature and concentration of the antibiotic produced. 



Two of the groups selected for this comparison are typically chromogenic, 

 being capable of producing brown to dark brown or almost black soluble 

 pigments on protein-containing media, due largely to the formation of the 

 enzyme tyrosinase (S. antibioticus and S. lavendulae) . One group is non- 

 chromogenic, although it produces a faint soluble brown pigment on certain 



