Genetic Recombination 

 in Bacterial Viruses 



N. VISCONTI, Carnegie Institution of Washington, 

 Cold Spring Harbor, New York 



At first sight the life cycle of a bacteriophage particle seems simple. 

 It is adsorbed to a bacterium, and after a characteristic period of time 

 called the latent period, which is 22 minutes for T2, the bacterium 

 bursts open, releasing several hundreds of particles identical to the 

 one adsorbed at the beginning. To the scientist concerned with the 

 biological problem of self-duplication, this is interesting. In order to 

 discover how and from what these particles are formed, we must see 

 what is going on in the bacterium during the latent period. There has 

 not been developed a method to look inside the bacterium without 

 disturbing the process of phage formation. Suppose instead that the 

 bacterium is broken before spontaneous lysis. What is found then? 

 In 1942 at Vanderbilt University, Delbriick and Luria started 

 experiments along this line of thinking. The problem was to break 

 the bacterium without damaging the phage or whatever was to be 

 found inside. One effective agent was known: that agent was the 

 phage itself. Suppose a bacterium is infected with two phages, Tl 

 and T2. Tl has a latent period of 13 minutes, T2 of 22 minutes. The 

 two phages will start to grow together, but after 13 minutes the 

 progeny of Tl will supposedly break the bacterium open. What will 

 happen to the progeny of T2? With this experiment began a scries 

 of unexpected results w hich led to the discovery of recombination. 

 In the bacteria infected with both Tl and T2, nothing happened at 

 13 minutes; at 22 minutes the cells burst, but only T2 was found in 

 the lysed culture. If, instead of a mixture of Tl and T2, only T2 had 

 been used, the result would have been the same. The explanation is 

 that T2 excludes Tl. Both phages are adsorbed to the same bacterium, 

 but only one can grow. If, instead of infecting simultaneously with 

 Tl and T2, an advantage of 4 minutes is given to Tl, many bacteria 

 will yield Tl but not T2. The bacterial culture as a whole may yield 



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