218 FRANCOIS JACOB 



in the population. During the multipHcation of such strains, bacterial 

 clones segregate which have lost one or more prophage alleles. Very 

 often, clones are found in which only the original maConii^ prophage re- 

 mains. Other clones exhibit various types of phage allele combinations. 

 Attempts to demonstrate some kind of diploidy for the Galh marker in 

 these strains were unsuccessful. After two successive isolations on 

 galactose-selective medium, colonies were grown in broth and streaked 

 on EMB galactose agar. All contained only Gal^ bacteria. These results 

 seem analogous to those found after mixed infection with two geneti- 

 cally labeled X phages (Appleyard, 19546; Jacob, unpublished results). 

 The results of this experiment show conclusively that the transduced 

 prophage can either recombine with, or be added to, the prophage of the 

 acceptor bacteria. Since the probability of being incorporated decreases 

 from the mi to the ms end of the X linkage group and since, in addition, 

 mi has no selective advantage over Ws in establishing lysogeny after in- 

 fection, it seems likely (although the data are statistically not very sig- 

 nificant) that the mi end of the X prophage is the closest to the Galh 

 locus. Although no definite conclusion can be drawn from the small 

 numbers of cases, the ratio of the probabihties of bringing either mi 

 alone or mi and Co together (3 : 9) is not in disagreement with the ratio 

 of the frequencies of recombination niiCo/coms found in crosses between 

 vegetative phages (4:9). 



DISCUSSION 



The experiments reported in this paper show that the phage material 

 present as a prophage in the donor bacterium can be transferred to an 

 acceptor bacterium by means of a transducing phage. The transduced 

 phage material can develop in the nonlysogenic acceptor bacterium when 

 experiments are performed at 37°. It seems likely, however, that this 

 phage material is transferred as a constituent of the donor bacterial 

 chromosome, i.e., as a prophage, since in transduction, as well as in 

 bacterial recombination, the same linkages between lysogeny and nutri- 

 tional markers are found. Moreover, at 20°, the transfer of lysogeny oc- 

 curs with about the same frequency as the transfer of nonlysogeny. 



In E. coli K12, two relative measures of linkage between two given 

 characters, such as threonine and leucine, can be obtained, one by trans- 

 duction and one by recombination. The relationship between these two 

 scales of measure is about the same when lysogeny is one of the char- 

 acters involved. In transduction experiments, lysogeny behaves there- 



350 



