108 



THE ACTINOMYCETES, Vol. I 



recovered by illumination with ^dsible light, 

 a phenomenon that came to be known as 

 ^'photoreactivation." 



A culture of *S'. flaveolus was treated with 

 x-rays in doses I'anging from 25,000 to ."^00, 

 000 roentgen units. In one experiment iS per 

 cent of the spores survived 100,000 r units, 

 and 0.03 per cent 300,000 r units. The sur- 

 Vw'A rate was in\'ersely proportional to the 

 dose. The following mutants were obtained: 

 (a) biochemically deficient strains which 

 grew well on nutrient agar but very poorly 

 or not at all on asparagine glucose agar; (b) 

 strains with pigmentation more intense than 

 or different from that of the wild type; and 

 (c) asporogenous strains. About 24 per cent 

 of the survi\'ing spores in a suspension 

 treated with 200,000 r units were mutants. 



One of the procedures for obtaining highly 

 potent antibiotic-producing strains consists 

 in combining ultraviolet or chemical treat- 

 ment of spores with single-colony isolation. 

 Another method takes advantage of the 

 frequently greater resistance of organisms to 

 the antibiotic they produce, as in the case 

 of streptomycin, in the plating out of cul- 

 tures in media containing increasing con- 

 centrations of the particular antibiotic; the 

 colony that will develop on the plate will 

 tend to represent more potent strains than 

 the original ones. Dulaney et at. presented 

 details of the first method, as shown in 

 Figure 46. The most variable characters in- 

 cluded color of spores and degree of sporula- 

 tion; surface and margin of colony, and 

 colony sectoring; amount and color of exu- 

 date on colony surface; amount and color of 

 soluble pigment released in substrate. There 

 was also marked variation in amount of 

 streptomycin produced, although no com- 

 plete correlation could be obtained between 

 the latter and the morphological type. Some 

 of the strains retained the capacity to gi\e 

 high streptomycin yields, and others lost it. 



According to Xewcomhe (Figs. 49 and 50) 

 exposure of spores of streptomyces to ultra- 



violet and gamma rays results in hereditary 

 changes affecting colony morphology and 

 pigmentation. These changes are largely 

 associated with instabilities that I'esult in 

 further variation during colony growth and 

 spore formation. These instabilities persist 

 indefinitely, giving rise to new variants hav- 

 ing their own patterns of instability. These 

 changes differ from gene mutations in that 

 they can be induced with much greater fre- 

 (}uency, and that gamma rays are as effective 

 as or more effective than ultraviolet irradia- 

 tion, suggesting chromosomal rearrange- 

 ments. Mutations are caused by treatment 

 with x-rays, ultraviolet, and cold, a period of 

 sensitivity during early spore germination 

 being common to all; in the last two treat- 

 ments, there is dependence on metabolic 

 activity. The phenomenon of photoactiva- 

 tion was studied further by Erokhina and 

 Alikhanyan. 



Horvath et al. observed that when an 

 antibiotic-producing strain of S. glohisporus 

 was grown in a sterile filtrate of the macer- 

 ated mycelium of another antibiotic-produc- 

 ing organism {S. globosus), there occurred, 

 after several repeated transfers, a change in 

 the morphological and physiological prop- 

 erties of the first organism. The newly pro- 

 duced strain retained its properties for a 

 considerable time. Cultivating actinomy- 

 cetes in media containing con\'allamin 

 changed the staining properties of the organ- 

 isms and the appearance of the colonies. 

 When grown in ordinar}^ media, such cul- 

 tures tended to return slowly to the original 

 stage (Hassegawa et al.). 



According to Krassilnik()^% the intra- 

 strain and intraspeci(\s antagonism among 

 antinomycetes is not just a bizarre property 

 but is highly significant in nature and can be 

 utilized for species characterization. This 

 phenomenon has a hearing upon the whole 

 problem of the significance of antibiotics in 

 the part played by actinomycetes in the cycle 

 of natui'c (Scriabin). 



