GENETIC IMPLICATIONS OF MUTATIONS IN S. TYPHIMURIUM 281 



In all, 249 separate auxotrophic mutants, of which 20 are different, were 

 isolated out of 459 tests. Most of these showed requirements for single amino 

 acids, but a few required the purine base adenine, and others showed alterna- 

 tive, and a small number, multiple requirements. 



A large number of tests involving growth of multiple mutant stocks in 

 mixtures followed by re-isolations have been made to test for possible fusion 

 and recombination as reported by Lederberg and others in the K 12 strain 

 of E. coli. Recombination has been found but it is unlike that in sexually 

 reproducing organisms. 



Detailed studies of the different auxotrophs requiring cysteine or me- 

 thionine show a step-like series beginning with loss of ability to reduce in- 

 organic sulphate, and continuing to the loss of ability to form methionine. 

 Many of these mutational steps are explainable as due to the inactivation of a 

 specific enzyme, but several require a complex pattern of chemical interac- 

 tions. 



Similar studies of the adenine auxotroph suggest that adenine may be a 

 source of histidine. 



Tests have been made to determine if antigenic specificity can be altered 

 by radiation, with negative results. However, an auxotrophic mutant has 

 been antigenically altered in two difTerent cases by the Edwards technique of 

 passing through absorbed immune serum. In each case, one of the antigens 

 was removed, and in one case another antigen was added. In both cases the 

 biochemical requirement of histidine was retained. 



It appears that the auxotrophic and antigenic series represent two quite 

 different and unrelated sets of mutations. 



