INVESTIGATIONS ON A LYSOGENIC BACILLUS MEGATERIUM 



We can now discuss the "activation" theory of Burnet and McKie. The 

 activation could be the consequence of a mutation. But since, as in the case of B. 

 megaterium, this activation is induced by conditions of the medium, it is simplest 

 to envisage, at least in the case of the bacterium which we have studied, that the 

 activation is the result of the suppression of a competition between the pro- 

 bacteriophage and a specific substance or particle. This is obviously but a 

 working hypothesis. 



According to unpublished observations of A. Lwoff, Louis Siminovitch, and 

 N. Kjeldgaard, the length of the latent period of the bacteriophage of B. meg- 

 aterium in the sensitive strain under the conditions of these experiments is 45 

 minutes. Thus, in the experiments of these authors, 45 minutes elapsed between 

 the moment of the inflection of the bacterial growth curves and the start of the 

 production of the bacteriophage, which lasted for 20 to 30 minutes. "It seems," 

 they write, "as if a factor, or an ensemble of factors, among which we know that 

 the aeration of the medium plays an important role, determines the condition 

 which sets off the production of the bacteriophages. This sudden drop in the 

 rate of growth is evidently related to the development of the bacteriophage, 

 but one does not know whether it is the effect or the cause or both cause and 

 effect." A. Lwoff, L. Siminovitch, and N. Kjeldgaard envisage that the factors of 

 induction act by modifying the relative speed of multiplication of the bacterium 

 and of the probacteriophage. The equilibrium is modified in an irreversible man- 

 ner once the number of probacteriophages surpasses a critical value. In order 

 to explain its clonal characteristics, it suffices to suppose that lysis does not take 

 place until several divisions have occurred. The problem of the nature of the 

 factors of induction and of the mechanism of their action shall be discussed in 

 a future communication which shall appear in these Annates . 



VIII. Definition of Lysogenic Bacteria 



Since the liberation of bacteriophages by the lysogenic strain 899 of B. meg- 

 aterium occurs by bacterial lysis, there exists an incompatibility between the pro- 

 duction of bacteriophages on the one hand and the survival and, a fortiori, 

 perpetuation of the bacterial individual on the other hand. In a "lysogenic" 

 strain, there are bacteria which multiply and other bacteria which produce and 

 liberate bacteriophages. 



A lysogenic culture producing bacteriophages can be transferred indefinitely, 

 but only under the condition that it includes bacteria which do not produce 

 bacteriophages. On the contrary, a bacterium producing bacteriophages is a 

 bacterium condemned to death. It is thus appropriate to distinguish between a 

 lysogenic culture and a lysogenic bacterium ; in case of the latter the production of 

 bacteriophages is but a potential faculty. For that reason we have proposed the 

 following definition: "A lysogenic bacterium is a bacterium which perpetuates 

 the capacity to form bacteriophages without intervention of exogenous bacterio- 

 phages." 



In the case of lysogenic bacteria, the bacteriophage perpetuates itself in the 

 form of the probacteriophages and not in the form of bacteriophage virus par- 



328 



