INVESTIGATIONS ON A LYSOGENIC BACILLUS MEGATERIUM 



eyes some hundreds of bacteriophage lyses. We have thus observed the lysis of 

 16, 8, 4, or 2 contiguous bacteria. But we have never observed the lysis of a 

 single member of the diplo-bacillus. This question shall be discussed in paragraph 

 VII. 



Discussion. J. Bordet and Renaux (1928), F. Burnet and M. McKie (1929b), 

 and E. WoUman (1936) envisaged that the bacteriophage is secreted by lysogenic 

 bacteria without the latter being destroyed. The problem of the mode of 

 liberation of bacteriophage by lysogenic bacteria was also discussed by J. 

 Northrop (1939) who, having noticed the appearance of bacteriophages during 

 the growth of lysogenic cultures, concluded that the bacteriophage "is produced 

 during the growth of bacteria and not during the lysis." M. Delbriick and 

 S. E. Luria (1942), on the basis of the observations of E. Cordts, which, to our 

 knowledge, have never been published, thought that lysogenic bacteria can 

 produce bacteriophages without lysis. 



It should be noted that in the experiments of J. Northrop the value of the ratio 

 of bacteriophages to bacteria was approximately 2. If, in the interval between 

 two divisions, three bacteria out of every hundred lyse, each liberating 72 

 bacteriophages, then the value of the ratio of bacteriophages to bacteria will be 

 216 to 97; that is to say, approximately 2. Lysis of 3% of the bacteria during an 

 interval of two divisions does suffice to account for the relative number of 

 bacteriophages and bacteria observed by Northrop. This lysis would entail only 

 a 3% reduction in the theoretical "growth rate." But it is difficult to measure 

 growth rate with greater accuracy than 5%. Unless a very high proportion of the 

 'bacteria lyses, no study of growth curves can thus furnish valid data relevant to 

 the mode of liberation of the bacteriophages. All that can be said is that, in the 

 experiments of Northrop, the bacteriophages are liberated during the growth of a 

 bacterial population. But it is impossible to rule out the lysis of a certain percent- 

 age of the bacteria. 



Our experiments thus bring proof that the bacteriophage produced by the 

 lysogenic B. megaterium is liberated by bacterial lysis. Until the third minute 

 prior to lysis no bacteriophage is liberated. For a long time bacteriologists have 

 observed the partial lysis of colonies of lysogenic bacteria. The majority of these 

 workers thought that this lysis was due to the bacteriophage. But we know that 

 lysogenic bacteria can lyse without necessarily producing bacteriophage. Cultures 

 of B. megaterium 899 lyse completely in peptone medium if they are deprived of 

 oxygen. This lysis begins as soon as anaerobiosis is established. The lysis does not 

 liberate bacteriophages. The fact that the colonies of a lysogenic bacteria lyse 

 partially or totally does not imply that this lysis corresponds to the production of 

 bacteriophages. A fortiori, it is not possible to conclude that under these condi- 

 tions the bacteriophage is liberated by the lysis of bacteria. 



Is it possible to exclude the hypothesis of a secretion of bacteriophages by 

 viable bacteria from the fact that in our experiments liberation of bacteriophages 

 took place only by bacterial lysis? In the case of sensitive Escherichia coli 

 infected by bacteriophage T2, the nucleus disappears between the fifth and tenth 

 minute after infection (Luria and Palmer, 1945-1946). If the disintegration of 



324 



