101 l>\l)I\rio\ lUOLOGY 



was sif^iiificantly lowci- in I he inadiuted series. No complex phaj^c- 

 resistant imitaiits were observed in the it radiated series, and, alth()up;h no 

 other biochemical re(jiiirements were obsciNCMl in the spontaneous 

 mutants, ti\'e biochemical r(M|uirements other than tryptophane were 

 noted in th(^ 1 14 radiation-induced mutants studied. These are the most 

 critical data bearing on this important (piestion and indicate that radia- 

 tion-induced mutations may be qualitatively different from those that 

 occur spontaneously. 



RADIATIOX-IXDUCED MUTATIONS I\ BACTERIA 



Stable heritable variation in colony morphology, cellular morphology, 

 and pathogenicity were observed by Henri (1914) among the surviving 

 cells of B. anthracis cultures exposed to ultraviolet radiation. In addi- 

 tion, unstable variants occurred which reverted to the normal type. 

 Stable variants were produced in numerous experiments and appear to 

 have been bona fide mutations although, of course, the underlying cause 

 was not proved to be genie. 



Shortly after Muller's announcement of the mutagenic effect of X rays 

 in Drosophila (1927), Rice and Reed (1931) studied I'ough-to-smooth 

 variation in a bovine strain of Mycobacterium tuberculosis irradiated with 

 88-kvp X rays. Their results are hard to evaluate in that the rough-to- 

 smooth change occurs spontaneously and the smooth forms are quite 

 unstable. Haberman and Ellsworth (1940) qualitatively demonstrated 

 that X rays increased the so-called "dissociative" changes in .S. aureus 

 and 8. marcescens. 



The first quantitative study of X-ray-induced mutations in bacteria 

 was that by Lincoln and Gowen (1942) in which various colonial charac- 

 teristics of Phytomonas stewartii were utilized. The data show clearly an 

 increase in the frequency of mutations among the cells surviving X irradi- 

 ation, and the rate of mutation for the three major characteristics studied 

 was about 3.7 X 10"** per character per roentgen. Croland (1943) 

 observed a hinidredfold increase in mutants per 10^ cells in studies of the 

 succinate-miiuis to succinate-positive mutation in Moraxclla hvoffi with 

 X rays. He observed an increase in the absolute number of mutants as 

 well as in the proportion of mutants among the survivors. 



Biochemical mutants that affect specific syntheses were reported by 

 Roepke ct al. (1944) and Gray and Tatum (1944) following X-ray treat- 

 ment. Since that time, numerous in\(^stigators have succeeded in iso- 

 lating biochemical mutations in various species of bacteria. 



The work of Demerec and Latarjet (1946) and Anderson (1951b), who 

 have published the most precise ciuantitativo studies of induced mutations 

 in bacteria, will he discussed later. 



Burkholder and Giles (1947) induced biochemical mutations with 

 ultraviolet and X-ray treatment of B. subtilis spores, and Devi ct al. 



