ZINDER AND LEDERBERG 



variation developed spontaneously and 

 independently between the "descend- 

 ing" lines. The genus Salmojiella in- 

 cludes a group of serotypes which 

 share a receptor for S. typhnnurium 

 FA. Other receptor groups have yet to 

 be sought. Within such groups it 

 should be possible to evolve in the 

 laboratory other new serot^-pes com- 

 parable to the antigenic hybrid of S. 

 typhi and S. typhijmirium. 



Several different bacterial genera 

 have been intensively studied with re- 

 gard to modes of genetic exchange. 

 Each of the several known systems dif- 

 fers in details that enlarge our notions 

 of bacterial reproduction and heredity. 



ACKNOWLEDGMENTS 



The authors are indebted to a num- 

 ber of workers cited in the text for 

 providing cultures and other materials. 

 They are especially obligated to Dr. 

 P. R. Edwards, Public Health Ser- 

 vice Communicable Diseases Center, 

 Chamblee, Georgia, for patiently pro- 

 viding innumerable cultures, sera, anti- 

 genic diagnoses, and counsel. 



SUMMARY 



When Sal?no7iella typhimurium is 

 grown in the presence of a variety of 

 mildly deleterious agents, especially 

 weakly lytic phages, it produces a 

 filtrable agent (FA) capable of trans- 

 ferring hereditary traits from one 

 strain to another. 



Individual filtrates may transduce 

 many different traits, but no more than 

 one in a single bacterium. The activi- 

 ties of a filtrate parallel the character- 

 istics of the donor cells. Nutritional, 

 fermentative, drug resistance, and 

 antigenic characters have been trans- 

 duced. The new^ characters are stable 

 after many generations of subcultures. 



FA is resistant to such bacterial dis- 

 infectants as chloroform, toluene, and 

 alcohol and to such enzymes as pan- 



239 



creatin, trypsin, ribonuclease, and des- 

 oxyribonuclease. The size of the FA 

 particle, as determined by filtration 

 through gradocol membranes, is about 

 0.1 micron. Adsorption of FA is rapid 

 and, among various serotypes tested, 

 is correlated with the presence of so- 

 matic antigen XII. 



The maximum frequency of trans- 

 duction for any one character has been 

 2 X 10-^, a limit set by saturation dur- 

 ing adsorption. Some inter-type trans- 

 fers have been observed. For example, 

 the / flagellar antigen from SalmoJiella 

 typhimiirmm has been transduced to S. 

 typhi to give a new serotype: IX, XII; 

 /, — . Genetic transduction in Salmo- 

 nella is compared and contrasted with 

 "type transformation" in Hemophilus 

 and the pneumococcus and with sexual 

 recombination in Escherichia coli. 



REFERENCES 



Alexander, Hattie E., and Leidy, Grace 1951 

 Determination of inherited traits of H. in- 

 finenzae hv desoxyribonucleic acid frac- 

 tions isolated from tvpe-specific cells. /. 

 Expf/.Mei. 93:345-359. 



Austrian, R., and MacLeod, C. M. 1949 Ac- 

 quisition of M protein through transforma- 

 tion reactions. /. Exptl. Med. 89:451-460. 



Avery, O. T., MacLeod, C. M., and Mc- 

 Carty, M. 1944 Studies on the chemical 

 nature of the substance inducing transfor- 

 mation of pneumococcal types. /. Exptl. 

 Afei. 79:137-158. 



Bacon, G. A., Burrows, W. W., and Yates, 

 Margaret 1951 The effects of biochemical 

 mutation on the virulence of Bacteriu?n 

 typhosum: the loss of virulence of certain 

 mutants. Brit. J. Exptl. Path. 32:85-96. 



Bawden, F. C. 1950 Plant viruses and virus 

 diseases. Chronica Botanica Co., Waltham, 

 Mass. 



Boivin, A. 1947 Directed mutation in colon 

 bacilli, by an inducing principle of desoxy- 

 ribonucleic nature: its meaning for the 

 general biochemistry of heredit\'. Cold 

 Spring Harbor Symposia Quant. Biol. 12: 

 7-17. 



Boyd, J. S. K. 1950 The symbiotic bacteri- 

 ophages of Sahnonella typhimurium. J. 

 Path. B act. 62:501-517. 



