CLASSIFICATION OF THE ACTINOMYCETES 6 



curved. The curvatures range from mere waviness to the formation of 

 perfect spirals, which may be compact, in the form of fists, or long and 

 loose. 



The growth of streptomyces "colonies" on artificial media is smooth or 

 lichnoid, hard and densely textured, raised, and adhering to the medium. 

 The colony is usually covered completely or partially, in the form of spots 

 or concentric rings, by aerial mycelium, which may be variously pigmented, 

 depending on the species and on the composition of medium. In liquid 

 media, especially in shaken cultures, growth of a streptomyces is usually 

 in the form of flakes, which gradually fill the container, or in the form of 

 spherical growths or puff balls. It is the former type of growth that is most 

 desirable from the point of view of antibiotic production. 



Many of the cultures, either in the form of colonies on the surface of 

 solid media or as flaky growth in submerged culture, may undergo rapid 

 autolysis. The production of antibiotics usually corresponds with the lysis 

 of the cultures. Frequently the lysis is brought about by a phage, actino- 

 phage, which is injurious because of the premature destruction of the my- 

 celium. 



The analogy between the aerial mycelium and sporulation of species of 

 Streptomyces and those of certain fungi has frequently led to confusion in 

 the classification of actinomycetes as a whole. More recent evidence, no- 

 tably the sensitivity of actinomycetes to antibiotics and to specific phages, 

 as well as the nature of their circumscribed growth, tends to place the ac- 

 tinomycetes as a group, including the genus Streptomyces, closer to the true 

 bacteria than to the true fungi. 



Finally a word must be said about the "physiological races" of the strep- 

 tomycetes. These organisms undergo in culture certain qualitative and quan- 

 titative variations. The streptomycin-producing strain of S. griseus, for 

 example, has yielded two types of variants, one of which produced no aerial 

 mycelium and formed no streptomycin, and the other of which produced a 

 red pigmented vegetative mycelium aud formed another antibiotic (rhodo- 

 mycetin) but not streptomycin. The qualitative differences of the variants 

 are best expressed in the amount of antibiotic produced, which may vary 

 as much as a hundredfold for the same species. From the point of view of 

 antibiotic production, the following five subgroups of S. griseus may now 

 be recognized : (a) those that produce streptomycin (as well as certain other 

 antibiotics, such as cycloheximide and streptocin), (b) those that produce 

 grisein, (c) those that produce candicidin, (d) those that produce still un- 

 identified antibiotics, and (e) those that do not yield any antibiotic, at 

 least under the particular condition of culture. Whether all of these vari- 

 ants have originated from a single original species of S. griseus is a matter 

 of speculation. The limited evidence seems to point to the affirmative. 



