Ill) 



THE ACTINOMYCETES, Vol. II 



the species, the formation of nonmelanin 

 pigments, the ecology of the organisms, and 

 some of the biochemical properties (notably 

 antibiotic formation) have been utilized. 

 This is also true of their practical utiliza- 

 tion for the production of enzymes, vita- 

 mins, or antibiotics. 



It would appear that morphological prop- 

 erties might offer a natural and stable basis 

 for a system of classification of these organ- 

 isms. Unfortunately, certain characteristic 

 morphological features of the genus Strepto- 

 myces undergo variation, depending upon 

 the nutrition of the organisms and upon the 

 environment. This tended to suggest, at 

 first, the inadvisability of considering mor- 

 phology as the major basis for the classifica- 

 tion of the genus Streptomyces. This was true, 

 for example, of Drechsler's idea of consider- 

 ing the type of curvature 1 of the spiral-form- 

 ing aerial hyphae as a basis for classification. 

 It was also true of YVaksman's suggestion 

 that the mode of branching of the sporo- 

 phores might be used for this purpose. The 

 ideas of Krassilnikov (1941, 1949) in empha- 

 sizing the size and shape of the spore would 

 also meet with similar criticism. Flaig et al. 

 ( 195o), as well as Ett linger et al. (1958), pro- 

 posed use of the nature of the spore surface 

 as a species characteristic; unfortunately, 

 this property, depending ;is il does upon the 

 use of the electron microscope, has not been 

 readily enough established to enable the sep- 

 aration of the genus into groups and species. 



Certain morphological properties are 

 now, however, well recognized and can be 

 utilized for the separation of certain groups 

 of organisms belonging to the genus Strepto- 

 myces. Such groups possess sufficiently well 

 defined morphological features to differen- 

 tiate them from the rest of the genus. This 

 is true particularly of those forms that 

 produce radiating sporulating hyphae (verti- 

 cils), with straight or spiral-shaped branches 

 on the main sporophores or on the side 

 branches. This property makes it possible 



to distinguish these particular forms from 

 the majority of other species of Streptomy- 

 ces, which produce either straight, flexuous, 

 curved, or spiral-forming sporophores. Sev- 

 eral systems of classification of the genus 

 Streptomyces into series (Hesseltine et al., 

 1954; Shinobu, 1958b) took full advantage 

 of the verticil-producing property; Baldacci 

 (1959) went so far as to suggest placing the 

 latter into a separate genus. The separation 

 of the spiral-forming from the straight 

 sporophore-producing types into separate 

 groups has also been frequently suggested. 



In view of the above limitations, the only 

 conclusion that can be reached is that, for 

 the present at least, a logical system of 

 separation of the genus Streptomyces into a 

 number of distinct series should be based 

 upon a combination of several of the mor- 

 phological and physiological properties. It 

 is proposed here to divide the genus into 

 16 series. This system, likewise, is open to 

 criticism: (a) there is left, for example, con- 

 siderable room for a certain amount of over- 

 lapping in some of the major properties which 

 characterize the various series; (b) the posi- 

 tion of a species within a series is not always 

 well defined, and some of the species could 

 frequently be placed with as much justifica- 

 tion in one series as in another; (c) there is, 

 further, a lack of uniformity in characteriz- 

 ing the various series: in some instances 

 color of the aerial mycelium or of the sub- 

 strate growth is used, and in others the 

 formation of soluble pigments is emphasized. 



Fully recognizing the above limitations, 

 however, I feel that a sound basis has keen 

 laid, taking full advantage of the knowledge 

 now available, for dividing the genus Slr< pto- 

 myces into series. As further information 

 accumulates, the system can easily be modi- 

 fied, since it lends itself readily to various 

 changes and modifications. 



A detailed characterization of the various 

 series is presented here. Some of the series 

 are described in greater detail than others. 



