ANDRE LWOFF AND ANTOINETTE GUTMANN 



resistant culture contaminated by bacteriophages. But these arbitrary defini- 

 tions do not exclude lysogeny in the sense in which we have defined it ; lysogeny 

 in which the property to produce bacteriophage is hereditary. In 1925 J. Bordet 

 wrote: "The faculty to reproduce bacteriophages is inscribed into the very 

 hereditary weft of the microbe," and Burnet and McKie (1929b) expressed 

 exactly the same idea: "The permanence of the lysogenic character makes it 

 necessary to assume the presence of bacteriophage, or its anlage, in every cell of 

 the culture, i.e., it is a part of the hereditary constitution of the strain." 



No doubt the experiments on which this conclusion was based — which shall 

 be discussed in the course of this work — however suggestive they were, did not 

 bring the element of certainty. It is true that as late as 1949, in spite of numerous 

 works published on lysogenic bacteria, one still did not know the manner in which 

 lysogenic bacteria liberate the bacteriophage that they produce. Is the bacterio- 

 phage secreted by the bacteria in a continuous manner? Is it secreted at the 

 moment of division? Is it liberated by the lysis of certain bacteria? In the 

 absence of any facts, the majority of microbiologists envisaged, along with 

 Bordet and Renaux (1928), and with Burnet and McKie (1929b), that the 

 bacteriophage is "secreted" by the bacterium. But it is really of little importance 

 for the definition of lysogeny whether the bacteriophage is liberated in this or any 

 other manner. The important fact is the reproduction of a bacterium potentially 

 capable of producing a bacteriophage, that is to say the hereditary capacity to 

 produce a bacteriophage. Naturally this does not exclude the mode of liberation 

 of the bacteriophage from being worthy of our attention. 



J. Northrop (1939) established a parallelism between enzymes and bacterio- 

 phages, based on the observation that the concentration of bacteriophages in a 

 culture of lysogenic bacteria increases, like that of the enzyme gelatinase, in an 

 essentially parallel manner to the multiplication of the bacteria. But it is quite 

 evident that the interpretation which one can draw from such facts will be very 

 different according to whether, for example, in the interval of two divisions every 

 one of 100 individuals of a bacterial population liberates a bacteriophage, or 

 whether a single bacterium liberates 100 bacteriophages. 



The principal problems posed by the existence of lysogenic strains are the 

 following: 1. Can the faculty of producing bacteriophages really be perpetuated 

 without intervention of exogenous bacteriophages? 2. How do lysogenic bacteria 

 liberate the bacteriophages which they produce? 3. If the production of bacterio- 

 phages appertains to only a certain proportion of the bacteria, then what factors 

 induce the production of bacteriophages in a population of potentially lysogenic 

 bacteria? The experiments presented here in detail were summarized in four 

 preliminary notes (Lwoff and Gutmann, 1949-1950) ; they furnish a reply to the 

 first two questions. The third question was studied in collaboration with 

 L. Siminovitch and N. Kjeldgaard, and the relevant results shall be the subject 

 of a separate paper. 



II. Materials and Techniques 



It was evident a priori that the study of "mass cultures," as it is usually 



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