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THE ACTINOMYCETES, Vol. II 



Burkholder et al. (1954) were led to con- 

 clude that the species concepts formulated 

 by an individual investigator depend a great 

 deal upon the investigator's personal expe- 

 rience, and whether he is a "splitter" or a 

 "lumper." They suggested further that mi- 

 crobial species should be characterized by 

 multiple, readily recognizable, and reason- 

 ably stable properties; the history of the 

 cultures and the nature of the medium in 

 which they are growing are of prime im- 

 portance. 



With the genus Streptomyces gaining con- 

 siderable economic importance, the creation 

 of many new species based upon biochemical 

 properties, notably formation of antibiotics, 

 resulted in much confusion in the recognition 

 of some of the species. The use of various 

 mutagenic agents, such as irradiation, led to 

 the formation of new forms or strains which 

 are often markedly different in their nutrient 

 requirements and biochemical activities from 

 the mother cultures. 



According to this concept, in the classifi- 

 cation of a group of living organisms, no 

 single feature can be taken as the predomi- 

 nant character. Only when this is combined 

 with a group of other characters is one able 

 to separate the group into subgroups, no- 

 tably genera and species. In selecting a char- 

 acter, no matter what its importance in the 

 primary subdivision of a group of actino- 

 mycetes, one may begin with color; or 

 structure of aerial mycelium; or certain bio- 

 chemical reactions, which may comprise 

 proteolytic activities, utilization of carbo- 

 hydrates, production of antibiotics, or phage 

 sensitivity. The important thing is to select 

 a group of properties to characterize each 

 species, with fewer characters, perhaps only 

 one, such as antibiotic production, charac- 

 terizing varieties. One always encounters, of 

 course, the intermediate forms between the 

 species. Each investigator will have to decide 

 upon the basis of the combination of charac- 

 ters whether to place an unknown culture 



with one species or another. Thus the concept 

 of species-group or section has come into 

 being. As a further illustration one may take 

 S. griseus and S. griseinus, two species be- 

 longing to the S. griseus group; both are non- 

 chromogenic; the color of the aerial myce- 

 lium of both is similar; they are both similar 

 morphologically; yet they are different from 

 the standpoint of carbon utilization, phage 

 sensitivity, and antibiotic production. 



Flaigand Kutzner (1954), Kutzner (1956), 

 Baldacci (1959), and numerous others em- 

 phasized both physiological and morphologi- 

 cal criteria. Gause et al. (1957) emphasized 

 the color of substrate and of aerial mycelium 

 as well as morphology of sporulating hyphae. 

 Numerous new species and varieties were 

 described, although very few prior named 

 species were discussed or placed into their 

 system of classification. Many of these spe- 

 cies and varieties are no doubt synonymous 

 with previously described forms. 



With streptomycetes, the species are 

 linked together so gradually that it is very 

 difficult to say where one species ends and 

 another begins. The creation of "sections," 

 "groups," or "series" to occupy an inter- 

 mediate place between genera and species 

 may help in clarifying relationships, but it 

 does not do away entirely with the poten- 

 tial confusion in the creation of new species, 

 especially when the relation of such species 

 to those already established is not sufficient ly 

 understood. This confusion has led some in- 

 vestigators to question "whether the species 

 concept is tenable in microbiology, and if it 

 is not, what we are to substitute for it." It 

 has even been suggested that the idea of 

 static species must be abandoned in favor of 

 something more elastic. 



Even now, after many additional data 

 have accumulated concerning the morphol- 

 ogy of the actinomycetes, and after these 

 organisms have been separated into a num- 

 ber of genera, there is still no general agree- 

 ment concerning characterization of species. 



