

( ii \i> 1 1 u 25 



i K.i ri 25-2. Large and minute (period-sized) 

 colonics of Salmonella, representing complete 

 ami abortive transductions, respectively. (Cour- 

 tesy of P. E. Hartman. ) 



tional. Because the prototrophic gene prod- 

 uct is made, the cell is able to grow and 

 divide. Only one of the first two daughter 

 cells, however, receives the added chromo- 

 somal fragment, the exogenote. The daugh- 

 ter cell without the exogenote is able to grow 

 and divide only until the prototrophic gene 

 product received from the parent becomes 

 too scarce; on the other hand, the hetero- 

 genotic daughter cell can continue to grow 

 and divide, in turn producing only one het- 

 erogenotic daughter cell. In this way a mi- 

 nute colony is produced which contains a 

 single genetically-prototrophic cell. This has 

 been proved in a variety of cases and by 

 various methods.' This consequence of the 

 failure of complete transduction is called 

 abortive transduction. 



Hypothetically, the exogenote in an abor- 

 tive transduction has two possible fates: the 



exogenote might eventually be lost; or it 

 might be integrated, resulting in a complete 

 transduction. Regardless of its ultimate 

 fate, the exogenote is considered to be ge- 

 netic in nature, even though it does not self- 

 replicate. Remember, however, that sell- 

 replication is an assumed characteristic of 

 the total genetic material: this capacity was 

 not required when a ^nc was first defined 

 (p. 33). 



In most transduction studies, an excess 

 of phage is used: that is, each cell is infected 

 with more than one phage particle. In such 

 experiments, it is always found that trans- 

 duced cells become lysogenic simultaneously. 

 Thus, the cell transduced receives not only 

 the exogenote but an apparently-complete 

 genome of a phage as well — the former re- 

 sulting in genetic recombination for one or 

 more host markers; the latter in lysogeny 

 and immunity. The phage particle whose 

 contents make the host cell lysogenic need 

 not be the same particle which introduces 

 the exogenote, since high concentrations or 

 multiplicities of infecting phage are used. 

 and, on the average, each host cell is pene- 

 trated by the contents of two or more phage 

 particles. Consequently, one particle might 

 furnish the exogenote, and another might 

 cause lysogeny and immunity. Using low 

 concentrations of phage to obtain low mul- 

 tiplicities so that almost no bacterium can 

 be infected by more than one phage, it is 

 possible to prove that, at least in some cases, 

 only one phage particle is needed per trans- 

 duction. It is found. 7 moreover, that when 

 a single phage attacks a susceptible bac- 

 terium, the virus can usually produce only 

 one of three mutually-exclusive effects on 

 its host — namely, lysis, lysogeny, or trans- 

 duction. 



E. coli strain K12 is normally lysogenic 

 for the temperate phage lambda (A). An- 

 other strain of /:. coli is nonlysogenic, that 



,; By B. A. I). Stocker, J. Lederberg, and N. D. 

 Zinder. and by H. Ozeki (1956). 



By J. N. Adams and S. E. Luria. 



