INVESTIGATIONS ON A LYSOGENIC BACILLUS MEGATERIUM 



The results presented below correspond to a study of 104 groups of bacteria: 



Number of drops 104 



Initial number of bacteria 295 



Final number 947 



Number of drops where lysis was observed 3 



Number of lysed bacteria 4_|_24-8 



Total of bacteria lysed I4 



The number of bacteria used was relatively restricted, but one can nevertheless 

 infer that, in certain experiments, the proportion of bacteria producing phage was 

 less than 5%, while in others, this proportion represented a quarter, or even a 

 third, of all the bacteria used. 



Discussion. The Mutation Hypothesis. The fact that only a certain proportion 

 of bacteria produced bacteriophages poses the problem of the nature of the factors 

 which induced a lysogenic bacterium to produce bacteriophages. If a sensitive 

 mutilat is mixed with bacteriophages, one observes the lysis of some of the cells 

 and the growth of resistant lysogenic colonies. The statistical analysis of the 

 phenomenon, such as has been carried out by M. Dulbriick and S. E. Luria 

 (1942), for E. coli, has not been carried out, and it is impossible to state that the 

 resistant bacteria represent spontaneous mutants. This is possible, or even 

 probable. One could envisage the hypothesis that this mutation from sensitiv- 

 ity to resistance is reversible. In the case of a lysogenic bacterium the mutation 

 from resistance to sensitivity would create conditions which permit "inactivation" 

 of the potential bacteriophage and of the lysis of the bacterium. One, thus, 

 conceives the idea that the mutation could intervene in determining the 

 production of bacteriophages by certain lysogenic bacteria. 



The mutation rate is generally independent of the conditions of the medium, 

 and we have seen that the percentage of bacteria which lyse varies from .5 to 

 30%. But this does not necessarily exclude the mutation hypothesis. It is, in 

 fact, conceivable that this variability is the result of the simultaneous coming 

 into play of a high mutation rate and of selection. We would invoke the clonal 

 character of the lysis in support of this hypothesis. Let us recall that we never 

 observed the lysis of a single member of a diplo-bacillus, and that we have 

 sometimes seen the lysis of all of the bacteria in the same filament. This could be 

 interpreted in the following manner: Only the descendants of certain mutants 

 lysed, while there occur from 1 to 4 divisions between mutation and lysis. This 

 hypothesis is not incompatible with the hypothesis of induction. One could see, 

 in effect, that the mutation affects only a genotypic factor, and that the latter 

 does not express itself by the production of bacteriophages except under specific 

 conditions of the medium. It is, however, the study of the kinetics of the 

 production of bacteriophages, which shall now be presented, which allows one to 

 exclude the hypothesis of the intervention of a mutation. 



The Induction Hypothesis. The behavior the B. megaterium in microdrops has 

 given us the impression that the production of bacteriophages must depend, in 

 part, on the previous history of the bacteria, and the hypothesis was envisaged 



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