324 Pierre Fredericq 



phosphorus. Its X-ray inactivation curves indicate a mole- 

 cular weight somewhere between 60,000 and 90,000 (Latarjet 

 and Fredericq, 1955). 



Colicinogenic properties are extremely stable hereditary 

 characteristics. The V coli, isolated by Gratia in 1925, still 

 produces the same colicin today, and many strains studied 

 for over 10 years showed no variation in their colicinogenic 

 properties. In view of their hereditary stability and of their 

 constancy, colicinogenic properties must be governed by 

 genetic factors which induce colicin synthesis and ensure their 

 genetic continuity. The hereditary stability, however, is not 

 absolute. Colicinogenic strains may show variations in the 

 amount of colicin produced, and even yield rare mutants 

 which have permanently lost their colicinogenic properties 

 (Fredericq, 1948^). 



The genetic factors governing colicin production can be 

 transferred from a colicinogenic strain to a non-colicinogenic 

 one in mixed culture (Fredericq, 1954a). The efficiency of 

 this transfer is quite variable and a selective technique is 

 often required to demonstrate it. The transfer may be from 

 colicinogenic Esch. coli strains to other non-colicinogenic 

 but related strains such as other Esch. coli, paracoli, Sh. 

 sonnei (Fredericq, 1954a), or even Klebsiella pneumoniae, 

 Salmonella typhi and Salmonella para B (Hamon, 1956b). 

 Conversely colicinogenic Sh. sonnei or S, para B may also 

 transfer this property to Esch. coli strains. 



Strains made colicinogenic in this way retain all charac- 

 teristics which marked the original non-colicinogenic strain 

 and differ only from it by the newly acquired colicinogenic 

 property. This isolated transfer of a single trait by mixed 

 culture of two strains comes within the range of phenomena 

 which Lederberg (1952) called transduction. This term is 

 often used in the restricted sense of a genetic transfer by 

 means of phage particles but, as far as can be judged, phages 

 play no part in the transduction of colicinogenic properties 

 (Fredericq, 19545). 



Transduction is specific for each colicin considered and 



