CLASSIFICATION OF STREPTOMYCES SPECIES 



153 



Whether this practice should be extended 

 and recognil ion thus be given to the capacity 

 to form sclerotia or to the ability to form 

 verticils by certain Streptomyces species, 

 thus placing them in separate genera, re- 

 mains to be determined. The author's sug- 

 gestion of many years ago thai the structure 

 of the sporophores (straight versus spiral- 

 forming, closed versus open spirals, tuft- and 

 verticil-producing) be used in characterizing 

 certain species or species-groups is gaining 

 wider recognil ion, though some investiga- 

 tors do not consider this a sufficiently con- 

 stanl property for the major subdivision of 

 the genus and suggest thai it lie left for 

 secondary characterization. The shape and 

 size of the spores appear to he less signifi- 

 cant properties, although the surface* of the 

 spores, as delected by the electron micro- 

 scope, has been gaining approval. 



Among the most annoying characteristics 

 of the genus Streptomyces are: (a) the loss of 

 capacity by certain species to produce aerial 

 mycelium, and (b) the overlapping property 

 on the part of certain species of Nocardia to 

 produce an aerial mycelium thai cannot he 

 differentiated from that of Streptomyces. It is 

 true, however, that cultures of Streptomyces, 

 even if they have lost the capacity to pro- 

 duce aerial mycelium, can still he recognized 

 by the si ructure of their substrate mycelium 

 and by certain cultural and physiological 

 properties. The latter include the nature of 

 their soluble pigments, their ability to 

 liquefy gelatin, hydrolyze starch, invert 

 sucrose, and coagulate and peptonize milk. 

 Some strains that have lost the capacity to 

 produce aerial mycelium may regain this 

 property if they are grown in sterile soil or 

 in special soil media, or are subjected to 

 other special treatments. 



The growth of cultures of Streptomyces 

 that have lost the capacity to produce aerial 

 mycelium is often colorless, though some- 

 times pigmented; it is smooth or lichenoid, 

 leathery, compact, with a shiny surface. 



Some produce a soluble brown pigment. 

 Some are able to form antibiotics. On the 

 assumption thai such cultures, because they 

 do not form aerial spores, should be con- 

 sidered as sterile, Krassilnikov designates 

 them as trinomials with a third component 

 of the name "sterilis." This is analogous to 

 Fungus sterilis among the fungi. Certain 

 such species are included in the presenl 

 classification; others may be considered as 

 typical nocardias and have been transferred 

 to that genus. 



Characterization of Streptomyces Spe- 

 cies 



Among the properties to receive major 

 consideration in describing individual spe- 

 cies are the following: 



1. Morphological properties: These include 

 formation and nature of substrate (vegeta- 

 tive) growth and of aerial mycelium, manner 

 of sporulation (spiral formation, verticil 

 formation), nature and surface of spores. 



2. Cultural characteristics. These com- 

 prise color and color changes of substrate 

 growth and of aerial mycelium, and forma- 

 tion of soluble pigments on synthetic and 

 organic media. The most significant of these 

 pigments are the melanins or melanoids pro 

 duced in media containing tyrosine or pro- 

 teins and peptones. The brown to black 

 pigments produced in such media by certain 

 species of Streptomyces are said to designate 

 melanin-positive as opposed to melanin- 

 negative reactions, or tyrosinase-positive 

 versus tyrosinase-negative reactions. In view 

 of the fact, however, that lew of the older 

 investigators tested this read ion in tyrosine- 

 free media, it is more desirable to use the 

 designations chromogenic (melanin + ) or 

 Qonchromogenic (melanin — ). In this case, 

 chromogenicity refers specifically to the 

 formation of brown to black pigments on 

 protein-containing media. 



:;. Physiological and biocht mien/ prop, rtu s. 

 These include: proteolytic activities, such as 



