ZINDER AND LEDERBERG 



prototroph selections were nonfer- 

 menters and the papillae selections 

 acted only upon the one sugar and 

 were auxotrophic. All of the trans- 

 duced cells were still streptomycin re- 

 sistant. 



The foregoing experiment was re- 

 peated on double sugar agar. Individ- 

 ual papillae fermented either galactose 

 or xylose and were all auxotrophic. 

 Because of a slight difference in tex- 

 ture it was possible to differentiate the 

 two kinds of papillae directly on the 

 indicator plate. Entire papillae were 

 picked and transferred to the alterna- 

 tive sugar and to minimal agar. Among 

 the many tested, no mixed papillae 

 were found. Any such could be de- 

 tected by this rigid selection. 



From these experiments, we con- 

 clude that an FA filtrate has many 

 activities, producing many different 

 transductions (but no more than one 

 per cell) that result in singly trans- 

 duced clones. 



We have observed no linked segre- 

 gations such as had been found in E. 

 roll recombination. The singular ac- 



D 



tivity of FA mig^ht still be reconcilable 

 with a gametic interpretation if the 

 failure to show linkages were due to 



229 



structural differences in the chromo- 

 somes of the parents. Alternatively, 

 FA might have been considered in 

 terms of a nonspecific mutagen with 

 independent action on different fac- 

 tors. Further experiments have disqual- 

 ified both of these views beyond 

 reasonable doubt. 



LT-7 served as an efficient donor 

 and receptor of FA and was chosen for 

 the study of the intrastrain transfers 

 and to test these considerations (see 

 table 1 for its markers). To be certain 

 of the source of the FA employed, it 

 was prepared (as described previ- 

 ously) without external bacterial oi 

 viral influences. FA was prepared from 

 SW-184 (prolineless), SW-188 (me- 

 thionineless), and SW-191 (leucine- 

 less). Each preparation was assayed for 

 transduction from auxotrophy to 

 prototrophy of each of the three LT-7 

 auxotrophs and LA-22 (control for the 

 presence of any activity). The prepa- 

 rations had fairly uniform activity on 

 LA-22. However, FA from each of 

 the three LT-7 auxotrophs could 

 transduce the other two but not its 

 source culture (table 3). FA thus con- 

 forms to the genotype of the cells 

 from which it comes. Several galac- 



Table 3 



The effect of FA from LT-7 and its derivatives upon LT-7 derivatives 



* Presumably spontaneous reverse mutations. 



Figures are transductions from auxotrophy to prototrophy per plate. 



tose-negative mutants were obtained 

 in each of the three auxotrophs. None 

 of several thousand transduced pro- 

 totrophs was galactose positive. FA, 

 from SW-184 (prolineless), when 



plated with SW-188 (methionineless) 

 on minimal agar supplemented with 

 proline, resulted only in proline inde- 

 pendent colonies (prototrophs). Com- 

 parable results have been obtained 



