MICROBIOLOGY 



INDUCTION OF BACTERIOPHAGE LYSIS OF AN ENTIRE 

 POPULATION OF LYSOGENIC BACTERIA' 



by 



Andre Lwoff, Louis Siminovitch, and Niels Kjeldgaard 



Presented by Robert Courrier 



In a culture of lysogenic Bacillus megaterium, some bacteria multiply 

 without liberating bacteriophages and perpetuate the lysogenic strain, 

 while others produce bacteriophages which are liberated by lysis. ^ Under 

 normal conditions of exponential growth, only a very small percentage 

 of bacteria produce bacteriophages.^'^ 



We have succeeded in inducing bacteriophage lysis of an entire popula- 

 tion of lysogenic bacteria by means of irradiation by ultraviolet light. 



B. megaterium is grown in a yeast extract medium.- During the expo- 

 nential growth phase, when the number of bacteria has attained 34 X 10® 

 per ml., a 2 mm layer of the culture is irradiated with ultraviolet light from 

 a high pressure mercury vapor lamp, which delivers to the surface of the 

 liquid an energy of 2000 ergs per mm- per minute of radiation of wave 

 length 2537 A. The culture is then shaken at 37° and its optical density 

 (O.D.) increases for about 80 minutes. The normal growth rate, that is 

 to say the number of doublings per hour, is 3. Immediately after irradiation 

 the growth rate is in the neighborhood of L5. At about the 80th minute, 

 when the O.D. has increased by a factor of 3 to 4, bacterial lysis takes 

 place: the culture clears in 40 to 80 minutes. The fraction of bacteria 

 surviving is usually less than 10~*. Lysis is accompanied by the liberation 

 of about 70 to L50 bacteriophages per bacterium. Analogous results have 

 been obtained with irradiation for 20, 30, 90, or 120 seconds. 



A culture growing in synthetic medium and similarly irradiated from 1 to 

 60 seconds does not lyse. On the other hand, if a culture growing in yeast 

 medium is centrifuged, resuspended in synthetic medium, and then ir- 

 radiated for 5, 10, 20, or 30 seconds, bacteriophage lysis does take place. 



Translated from the French and reprinted by permission of the 



authors and the Imprim^rie Gauthier-Villars from the Comptes 



Rendus des Seances de l'Academie des Sciences, 231, 



190-191 (1950). 



332 



