EFFECTS OF RADIATION OX IJACTERIA 



409 



a quantitatively equal effect on the purineless reverse mutation, it does 

 not seem to be a major factor in the induction of streptomycm-dependent 



reverse mutation. 



Demerec et al. (1952) have studied the reverse-mutation response ot H 



2400 



2200 



2000- 



1800 



-II X 10 



o 





3 



o 



Q 



1600- 



1400 



1200 



1000 



800 



600- 



400 



200- 



SURVIVAL RATIO, N/N^ 



Fig 10-13 Rate of X-rav induction of back mutations as a function of survival ratio 

 Left scale, comparison of the back-mutation rates to streptomycin nondependence of 

 the streptomycin-dependent strain irradiated in oxygen (curve I) or m nitrogen 

 (curve II). Right scale, comparison of the back-mutation rates to purme nonde- 

 pendence of the purineless strain irradiated in oxygen (curve III) or m nitrogen 

 (curve IV). {Anderson, 1951b.) 



mutant strains of E. coli to a variety of mutagenic treatments. The most 

 striking observation was that in four of the strains the spontaneous rate of 

 back mutation could not be increased by any of the mutagenic treatments 

 which included X and ultraviolet radiation, manganous chloride, and 

 ^-propiolactone. In addition, the quantitative response of the other 

 strains to ultraviolet and manganous chloride varied differentially. 



It seems clear that all bacterial mutations do not exhibit the same 



