Chapter IV — 73 — Variations and Mutations 



of sectors pigmented red among orange-yellow strains. These saltations, 

 are accompanied by morphological, cultural, and physiological characters 

 which are quite different from those of the mother cultures. These 

 new strains are so distinct that they might be considered new species, 

 in accordance with the accepted systems of classification. 



Stable mutants or saltants were obtained and studied in detail by 

 Kriss (242) and Krassilnikov (234). Jensen has shown (188) that 

 under the influence of ultraviolet rays or even spontaneously, two strains 

 of Nocardia isolated from Australian soils gave rise to new forms, some 

 of which resembled t\'pical species of Streptowyces and others of which 

 were closer to the mvcobacteria. Jensen (191) also observed that under 

 the influence of LiCl mycobacteria gave rise to forms that might be con- 

 sidered as species of Nocardia. 



Recentlv, extensive investigations have been made of the effect of 

 ultraviolet radiations and x-ravs in inducing mutations of various species 

 of Streptomyces. Savage (385) reported that ultraviolet rays were 

 less mutagenic than the x-ravs, the harder rays of 0.710A and 0.210A 

 wave lengths being most efficient. Mutation rates increased with kill- 

 ing rates up to 99.9 per cent of killing. When doses of 1,000,000 roent- 

 gens were used, as high as 50 per cent mutation rates were observed on 

 morphological properties and 40 per cent on streptomvcin production. 



Bv means of x-rav and ultraviolet light irradiations, Kellner (213) 

 found that most antibiotically inactive cultures gave rise to antibiotic- 

 producing mutants. Of the greatest interest was the fact that a strain of 

 S. griseiis kept for a long time in the culture collection and which was 

 inactive antibioticallv was induced to form a mutant which produced 

 streptomycin. The frequency of active mutants ranged from 0.01 to 1.2 

 per cent; mutants obtained from the same parent culture varied in their 

 antibiotic spectra. The viability of conidia exposed to ultraviolet ir- 

 radiation could be recovered by illumination with visible light (214). 



The varations or mutations mav thus influence not only the species 

 characteristics but also the generic characters. Krassilnikov empha- 

 sized that these changes take place from the simpler to the more com- 

 plex forms, as from micrococci to mycobacteria, from mycobacteria to 

 nocardias, and from nocardias to streptomvces; the reverse phenomenon 

 occurs but seldom. This reasoning led Krassilnikov to the conclusion 

 that actinomycetes are present in natural substrates, such as soil, largely 

 in the form of micrococcus stages. 



Kriss (240, 242) recognized four types of variation— morphological, 

 cultural, physiological, and applied. These may be briefly summarized 

 as follows: 



Morphological xmriations.— Some of the morphological variations re- 

 ported may be considered here in further detail. Jensen (188) 

 described the production from single-cell cultures of Nocardia foly- 

 chromogenes of two different forms, one a rod-shaped or R-form, and 

 the other a filamentous or F-form. The R-form produces initially a 



