Bacteria: Recombination (K) 



379 



bacterium is stable and haploid with respect 

 to the Gal "locus" and produces per 100 

 thousand lambda only about one Ga/-carrying 

 lambda. Such progeny phage are said to 

 be capable of producing a low frequency of 

 transduction (LFT). About two thirds of the 

 transduced cells from LFT phage form clones 

 that are unstable with respect to Gal, i.e., 

 that segregate out the Gal genotype of the 

 recipient cell. In other words, a Gal bac- 

 terium transduced with lambda carrying Gal+ 

 is usually an unstable heterogenote, being 

 diploid and heterozygous for the Gal locus, 

 occasionally segregating Gal~ progeny. (It 

 should be noted that the merozygote pro- 

 duced by lambda transduction differs from 

 the merozygote produced by P22 in an abor- 

 tive transduction. In the latter case the 

 transduced segment is incapable of replica- 

 tion, whereas in the former case the trans- 

 duced segment can replicate, so that clones 

 of merozygotes may be produced.) When 

 infective lambda is induced from a lysogenic 

 individual merozygotic for Gah the transduc- 

 ing lysate may contain 100 times as many 

 phage carrying a Gal locus as does the lysate 

 of haploids. Such a crop of phage is capable 

 of what may be called a high frequency of 

 transduction (HFT). (There is a second 

 difference between generalized and restricted 

 transduction. In generalized transduction, 

 transducing phage may be obtained from the 

 lysate of nonlysogenic cells infected with free 

 phage, whereas this is not so in the case of 

 restricted transduction. Thus, in the case of 

 restricted transduction, transducing phage 

 are released only from lysogenic [haploid, or 

 merozygotic] bacteria.)^ 



From the results obtained by employing 

 different multiplicities and combinations of 

 transducing lambda (harvested from lysogenic 

 cells) and nontransducing lambda (harvested 

 soon after nonlysogenic cells are infected), it 



* The preceding account is based largely upon the 

 work of J. Lederberg, E. M. Lederberg, and M. L. 

 Morse, and of E. L. Wollman and F. Jacob. 



has been possible to prove,'' just as is true for 

 generalized transduction, that transducing 

 lambda is defective for a portion of the 

 lambda genome. What happens is that the 

 Gal loci being transduced probably replace 

 a segment of the lambda genome. The 

 transducing defective lambda particle (called 

 Wg) has retained certain phage properties 

 and lost others. Thus, when only a single 

 GcrZ-transducing particle is involved in an 

 infection, the particle is still capable of 

 eventually killing and lysing the cell. But it 

 has lost the ability to replicate and produce 

 infective phage progeny, so that the prophage 

 it forms must be defective. Also, such a 

 particle can only rarely lysogenize its host. 

 This means the host is only rarely immune to 

 further infection with lambda. Accordingly, 

 a cell infected by such a defective lambda is 

 still subject to infection by nontransducing 

 phage, whose additional presence (1) makes 

 the host lysogenic and (2) contributes a 

 function which permits the defective prophage 

 to multiply. At the time of lysis of such a 

 doubly infected cell, infective phages of both 

 nontransducing and transducing ability are 

 liberated. This situation is similar to that 

 already described in Salmonella which cannot 

 be lysed or lysogenized if infected by a 

 single transducing particle but which can 

 demonstrate either of these characteristics if 

 the host is also infected with one or more 

 normal, nontransducing P22 phage particles. 

 Transformation is not known to occur in 

 E. coli, probably due to some difficulty in 

 DNA penetration. One would predict, how- 

 ever, if the DNA of a defective lambda were 

 isolated and somehow introduced into a cell, 

 that it would sometimes behave as a trans- 

 forming principle with respect to Gal loci. 

 Even if naked DNA does not penetrate E. coli 

 by itself, it might be hoped that it would 

 adhere to the outside of a nontransducing 

 phage, and enter the host at the time the 



5 By W. Arber, G. Kellenberger, and J. Weigle(I957), 

 and by A. Campbell. 



