. The actinomycetes. Actinomycetales. 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.
. The actinomycetes. Actinomycetales. 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\ 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
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