84 



THE ACTINOMYCETES, Vol. II 



be mislabeled; seven were listed temporarily 

 as intermediates between the two genera. 



The differentiation between Streptomyces 

 and the other genera of actinomycetes is 

 not very difficult. The formation of aerial 

 mycelium and the manner of sporulation 

 are markedly distinct for Streptomyces as 

 compared to Micromonospora. Species of 

 Thermoactinomyccs also produce an aerial 

 mycelium, similar to that of species of 

 Streptomyces, but they form single spores, 

 similar to those of Micromonospora. The 

 other thermophilic genera, as well as the 

 genera Waksmania (Microbispora*), Actino- 

 planes, and Streptosporangium also can be 

 differentiated from Streptomyces, as shown 

 in Chapters 8 to 1 1. 



Among the numerous species belonging 

 to the various genera of actinomycetes, 

 those of the genus Streptomyces are by far 

 the most important, largely because of their 

 wide distribution, their greater abundance, 

 and their ability to produce antibiotics and 

 vitamins and to carry out important chemi- 

 cal conversions. Hence a detailed considera- 

 tion of this genus is justified. 



Description of Genus Streptomyces 



Streptomyces species produce a well-de- 

 veloped mycelium. The diameter of the 

 hyphae seldom exceeds 1 .0 m and is usually 

 only 0.7 to 0.8 n- The hyphae vary greatly 

 in length: some are long with limited branch- 

 ing; others are short and much branched. 

 The substrate mycelium does not form cross 

 walls; it does not break up into rod-shaped 

 and coccus-like bodies. Reproduction occurs 

 by means of spores or by bits of mycelium. 

 Spores or conidia are formed in special 

 spore-bearing hyphae or sporophores which 

 arise from the aerial mycelium either mono- 

 podially or in the form of tufts or verticils. 



* Bol h designations were published, in different 

 journals, the same month and the same year. 

 Priority lias not been definitely established. 



The sporulating hyphae are straight or 

 curved. The curvatures range from mere 

 waviness to perfect spirals, which may be 

 compact, in the form of fists, or long and 

 open (Fig. 23). 



The spores of streptomycetes comprise 

 four types: smooth, warty, spiny, or hairy. 

 About one-third of the gray- to brownish- 

 spored species were found (Tresner et al., 

 I960) to form spiny, warty, or hairy spores; 

 the remainder were smooth-spored. All the 

 blue- to blue-green-spored forms had spiny 

 spores. White, yellow, cream, or buff types 

 had smooth-walled spores. All the pinkish- 

 tan-spored group had smooth spores, with 

 the exception of S. erythreus and S. pur- 

 purascens which had spiny spores. The con- 

 clusion was also reached that, because of 

 the variation of spore size and shape, those 

 properties are of limited usefulness for 

 taxonomic differentiation. 



The growth of Streptomyces "colonies'' 

 on artificial media is smooth or lichenoid, 

 hard and densely textured, raised, and ad- 

 hering to the medium. The colony is usually 

 covered completely or partially (in the form 

 of spots or concentric rings) by aerial my- 

 celium, which may be variously pigmented, 

 depending on the species and on the com- 

 position of medium. In liquid media, es- 

 pecially in shaken cultures, growth of strep- 

 tomyces is usually in the form of flakes, 

 which gradually fill the container, or in the 

 form of spherical growths; the former type 

 of growth is the more desirable from the 

 point of view of antibiotic production. 



Many of the cultures, eithei in the form 

 of colonies on the surface of solid media or 

 as flaky growth in submerged culture, may 

 undergo rapid lysis. The production of anti- 

 biotics usually corresponds with the lysis 

 of the cultures. Frequently, the lysis is 

 brought about by a phage, known as actino- 

 phage, which exerts an injurious or destruc- 

 tive effect upon the mycelium. 



