THE GROWTH OF BACTERIOPHAGE AND LYSIS OF THE HOST 



By M. DELBRUCK* 



{From the William G. KerckhoJ' Laboratories of the Biological Sciences, California Institute 



of Technology, Pasadena) 



(Received for publication, January 29, 1940) 



Introduction and Statement of Main Result 



Bacteriophage grows in the presence of living susceptible bacteria. In 

 many but not all cases the growth of phage leads finally to a lysis of the 

 bacterial cells, a phenomenon which in dense cultures manifests itself to 

 the naked eye as a clearing of the bacterial culture. The exact nature of 

 the connection between the growth of the phage and the dissolution of the 

 cells has been a subject of controversy since the original discoveries of 

 d'Herelle in 1917. 



D'Herelle believed that lysis is the process by which the phage, which 

 has grown within the bacterium, is liberated from the cell and dispersed in 

 solution. Many later authors, notably Burnet, have concurred with him 

 on this point. Last year Ellis and Delbriick (1) published detailed evi- 

 dence that phage liberation in B. coli occurs in sudden bursts and showed 

 that all the evidence was compatible with the assumption that in sensitive 

 strains the bursts of phage liberation occurred only if and when a cell is 

 lysed. 



Northrop and Krueger (3-5) on the other hand have developed ideas 

 along a somewhat different line in the course of their extensive research 

 with a strain of Staphylococcus aureus and a bacteriophage active against 

 it. Bordet (2) had put forward the conception that phage production 

 followed by lysis is a more or less normal physiological function of the 

 bacteria. In lysogenic strains where visible lysis never occurs it can be 

 put into close analogy with the production of an extra-cellular enzyme. 

 Northrop's and Krueger's work served to substantiate this view also in 

 their case where the phage growth leads finally to the dissolution of the 

 bacteria. In their view lysis of the bacteria is a secondary and incidental 

 activity of the phage. 



Krueger and Northrop (3) found first that clearing, if it occurs at all, 

 begins when a certain threshold value in the ratio total phage/bacteria is 



* Fellow of The Rockefeller Foundation. 



Reprinted by permission of the author and The Rockefeller 



Institute from The Journal of General Physiology, 23 (5), 



643-660, May 20, 1940. 



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