Chapter 7 



Classification of Streptomyces Species 



The difficulties encountered by an inex- 

 perienced investigator in identifying a 

 freshly isolated culture of a Streptomyces with 

 previously described species have been 

 brought out in the preceding three chapters. 

 No wonder an inexperienced worker soon 

 becomes discouraged and takes the easy path 

 of creating a new species or variety for 

 every newly isolated culture. This is es- 

 pecially true if such a culture produces an 

 antibiotic not previously described or an 

 apparently different form of a known anti- 

 biotic that he is anxious to patent or on 

 which he wishes to establish priority. Among 

 the significant factors that have contributed 

 to this rash of "new" species are: 



1. Inadequate description of previously 

 described species with which comparisons 

 are made 



2. Overlapping of the morphological and 

 cultural characteristics of strains or species 

 previously described. 



3. Variations in composition of the media 

 used in describing species. 



4. Failure to recognize natural variability 

 of different strains that might be included 

 in a single species. 



5. Idiosyncrasies of the particular inves- 

 tigator, and his tendency to be either a 

 "lumper" or a "splitter." 



In spite of these discouraging aspects of 

 the problem of identification of particular 

 organisms, classification and characteriza- 

 tion of Streptomyces species have recently 

 made considerable progress. Though various 

 criticisms have been directed toward it, the 



system of classification of actinomycetes 

 used in the seven editions of Bergey's Man- 

 ual still appears to be the most logical and 

 most workable, except for certain modifica- 

 tions that are now desirable. In every new 

 edition, advantage has been taken of the 

 accumulated information to modify this sys- 

 tem of classification, especially of the genus 

 Streptomyces. In this treatise, a complete re- 

 arrangement has been made in classifying 

 the species included in the genus Strepto- 

 myces, as compared with the last (seventh) 

 edition of Bergey's Manual. 



The thermophilic species of Streptomyces 

 have been placed in a separate series Thermo- 

 philus and transferred to Chapter 11, in 

 which all the thermophilic actinomycetes 

 are included. Species of Streptomyces iso- 

 lated from animal and plant infections, es- 

 pecially those for which pathogenicity has 

 not been established, have been distributed 

 throughout the genus, thus removing the 

 need for a major separation of these species 

 into saprophytic versus parasitic forms. 

 These properties are now given only sec- 

 ondary consideration in characterizing spe- 

 cies within the genus. It has further been 

 recognized and emphasized, time and again, 

 that it is most desirable to utilize morpho- 

 logical properties in defining and charac- 

 terizing species of Streptomyces, though in 

 some instances this could not be done with 

 any degree of assurance. 



New genera have been created, once cer- 

 tain well-defined morphological and physio- 

 logical properties suggested its advisability. 



I 52 



