1 BACTERIOPHAGES 



of a lysogenic strain of Bacillus megalerium were heated above 

 lethal temperatures for free phage particles without killing the 

 spores. Each spore on germination gave rise to a lysogenic cul- 

 ture. Similar conclusions had been reached from studies on a 

 lysogenic strain of Salmonella enteritidis by Burnet and McKie 

 (1929) who wrote that "the permanence of the lysogenic char- 

 acter makes it necessary to assume the presence of bacteriophage 

 or its anlage in every cell of the culture, i.e., it is a part of the 

 hereditary constitution of the strain." 



For many years the manner of release of phage particles from 

 lysogenic bacterial cells was a subject of dispute. One popular 

 theory proposed that the phage was secreted by the growing 

 bacterial culture in the manner of extracellular bacterial enzymes 

 (Northrop, 1939b). An alternative theory held that the oc- 

 casional disintegration of a bacterial cell liberated a number of 

 phage particles in a way that was already familiar to students of 

 the virulent phages (Burnet, 1929a). This question was finally 

 settled by the work of Lwoff and Gutmann (1950) who demon- 

 strated by the use of micromanipulator techniques that phage 

 particles were not secreted by multiplying lysogenic bacteria, but 

 appeared in groups simultaneously with the disintegration of 

 single bacterial cells. 



The recent revival of interest in lysogeny begins with impor- 

 tant reinvestigations of the phenomenon by Lwoff and Gut- 

 mann (1950), Bertani (1951), and the Lederbergs (1953). 

 These papers are all the more interesting because they record 

 three quite different experimental approaches. 



Lwoff (1953) lists the characteristic signs of lysogeny as fol- 

 lows: 



7. In a lysogenic culture lysogenesis is a property of every cell 

 and every spore. 



2. Bacteria of a lysogenic culture generally can adsorb the 

 mature phage produced by the culture, but are not damaged by 

 it. 



3. Lysis of lysogenic bacteria by enzymes, by other phages, or 

 by mechanical means does not liberate mature phage particles. 



