VAHIA'l'loXS. MITATIONS, AND ADAITATIONS 



105 



<;r()\vlh that in a shaken cnUurc undriwcnl 

 rapid lysis. This nonspoiuhitinji; slniiii could, 

 thcrol'oro, iiardly hv recognizable us typical 

 »S. griscus; it could almost he consideivd 

 either as ti strain of Xocardia or as Strcpto- 

 myces sterilis. Appleby (1947) considered this 

 to be a stable variant, in the nature of muta- 

 tion, rather than a temporary response to a 

 particular medium or a particular set of 

 conditions. The frecjuency of this mutant was 

 increased by ultraviolet irradiation of N. 

 griseus spores. Greater consideration of the 

 relationship between asporogenous and 

 sporulating types was suggested. J3ulaney 

 et al. found that some strains obtained from 

 nonsporulating single-colony isolates gave 

 relati\el.y high yields of streptomycin. 



2. Another variant produced a red pig- 

 mented substrate growth, although there 

 was no visible change in the nature of the 

 aerial mycehum. This variant lost its capac- 

 ity to form streptomycin but accjuired the 

 capacity to produce another antibiotic 

 (rhodomycetin), pigmented red and active 

 only upon gram-positive bacteria. When 

 freshly isolated from the natural substrate, 

 this culture would definitely not be con- 

 sidered as S. griseus. 



S. lavendulae was also found to yield a 

 number of variants (Waksman and Schatz, 

 1945; Waksman et al., 1951). These differed 

 in the amount and nature of soluble pig- 

 ment, in the nature and pigmentation of 

 their aerial mycelium, and in the production 

 of the antibiotic streptothricin. Two variants 

 of this organism were recognized: one gave 

 a l)luish colored substrate growth, a blue 

 diffusible pigment, and a lavender-colored 

 aerial mycelium with a slightly blue tinge; 

 the other formed a cream-colored substrate 

 growth, a soluble brown pigment in organic 

 media, and a lavender-colored aerial myce- 

 lium. Other variants obtained from this 

 (organism gave rise to cultures with white 

 aerial mycelium shaded pink; some were 

 de\-oid entirely of aerial mycelium, except for 



25 50 



100 



200 



DOSAGE, X 10 ROENTGENS 



Figure 51. Dosage of irradiation and mutation 

 frequency in S. flaveolus (Reproduced from: Kel- 

 ner, A. J. Bacteriol. 56: 463, 1948). 



a scant growth of sporulating aerial hj^phae. 

 These variants also differed in their ability 

 to produce the antibiotic. The conclusion was 

 reached that the formation of streptothricin 

 by S. lavendulae is associated wath its ability 

 to form aerial mycelium. 



Gau.se and Kochetkova studied the varia- 

 tions of a grisein-producing strain of a 

 streptomyces. Some of the strains formed 

 the pure antibiotic; others formed the anti- 

 biotic and a second factor; still others yielded 

 largely the second factor and very little of 

 the given antibiotic. \'arious transition forms 

 were also obtained. 



Krassilnikov (1957) obtained numerous 

 variants or mutants of the antibiotic-produc- 

 ing organisms S. griseus, S. coelicolor, S. 

 aureofaciens, and S. violaceus on treatment 

 with various mutagenic agents (radiation, 

 temperature, phages, antibiotics). A study 

 of these \'ai'iants or mutants revealed there 



