Microbiology 



Finally if yeast extract is added to a culture growing in synthetic medium 

 and the culture irradiated immediately for 10, 20, 30, or 60 seconds, no 

 lysis takes place. But irradiation carried out 20 to 40 minutes after addition 

 of the yeast extract (by which time the O.D. has increased by about 50%) 

 induces bacteriophage lysis. UV irradiation thus induces production of 

 bacteriophages only with bacteria which have grown for 20 to 40 minutes 

 in a complex organic medium such as yeast extract. 



Irradiation for 30 to 60 seconds of a non-lysogenic culture of B. mega- 

 terium growing in yeast extract does not appear to affect bacterial growth. 

 The lysis of the lysogenic strain is thus probably not a direct effect of the 

 UV irradiation. 



It has been demonstrated previously that all bacteria of a lysogenic 

 strain are capable of perpetuating the lysogenic character. ^ The experi- 

 ments described here, which have been complemented by studies of bacteria 

 irradiated and then isolated in microdrops, now demonstrate that under 

 certain conditions, all the bacteria of a lysogenic population are capable 

 of undergoing lysis with liberation of bacteriophages. 



'Supported by a grant of the National Institutes of Health of the United States of 

 America. 



2A. Lwoff and A. Gutmann, Ann. Inst. Pasteur, 78, 711-739, (1950). 



*A. Lwoff, A. Siminovitch, and N. Kjeldgaard, C'omptes rendus, 230, 1219-1221, (1950); 

 Ann. Inst. Pasteur, 79, 815 (1950). 



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