GENETICS OF RESISTANCE TO RADIATION IN <i>ESCHERICHIA COLI </i>

Abstract

MUTATION in Escherichia coli, leading to heightened resistance to ultra-A violet radiation and x-rays, was described in an earlier publication (WITKIN 1946).Evidence was presented that this mutation occurs spontaneously in cultures of the parent strain.I n the present paper, a more complete account of these preliminary investigations will be given, as well as additional experiments to clarify the genetic basis of resistance to radiation.This mutation is one of a number of bacterial variations which have been found, in recent years, to exhibit striking similarities to mutational changes in higher plants and animals.Since the standard techniques of Mendelian genetics have not been applicable to bacteria, these analogies afford the only available evidence that bacterial heredity is gene-controlled.Among the similarities between variations in bacteria and mutations in higher organisms which are most suggestive of a common underlying genetic basis are the following: ( I ) Many variations in morphological and physiological characters occurring in cultures of bacteria are transmissible, unchanged, through numerous generations, and are therefore considered to be stable and heritable (see, for example, MASSINI 1907, LEWIS 1933, SEVERENS and TANNER 1945).( 2 ) The spontaneous origin of certain stable and heritable variations, independent of the specific treatments used to detect them, has been proven in a few cases by means of special techniques (LURIA and DELBRUCK 1943, DE-MEREC 1945, RYAN, SCHNEIDER and BALLENTINE, 1946).(3) Different characters within a strain may vary independently of one another (REED 1937, AUDUREAU 1942).In one instance, the rate of mutation to a particular variant type was found to be the same for strains differing by one or more other mutational steps (DEMEREC and FANO 1945).(4) Physical and chemical agents known to be effective in increasing the rates of mutations in higher organisms have similar effects on bacteria (for the effects of x-rays, see HABERMAN and ELLSWORTH 1940, GRAY andTATUM 1944; for x-rays and ultraviolet, DEMEREC 1946; for mustard gas, TATUM 1946).The mutations induced by these agents