336 Discussion 



strains were obtained which were apparently still in the F~ state, as far 

 as one can judge from the absence of recombination with other F~ 

 strains. 



Hayes: Have you tried these transfer experiments using an Hfr strain? 



Fredericq: In preliminary experiments I have transferred a colicino- 

 genic property to an Hfr strain, but I have not yet had time to look for 

 the results of crosses. 



Lederberg: Can you do that experiment in which you have an F~ 

 colicinogenic mixed with an Hfr non-colicinogenic, and by contact 

 obtain colicinogenic Hfr? Is this process of transduction through 

 conjugation frequently reciprocal? This is where one parent is Hfr and 

 the other F". 



Fredericq: An F~ strain does not seem to be able to transfer its 

 colicinogenic property even to an F+ cell, or an Hfr cell. However, if 

 you make a prolonged mixed culture in broth you will get the transfer 

 because the F+ will first transform the F~ into F+, and then the transfer 

 between two F+ can be observed. 



Lederberg: Does it matter if the F~ strain that is used as a recipient is 

 carrying a marker for resistance to that culture ? 



Fredericq: It does not seem to matter. It is often easier to transfer 

 to a non-colicinogenic strain which has the corresponding receptor 

 because there is already a selection for transduced cells as they are 

 immune to that particular colicin. 



Lederberg: How frequent is the transfer compared, for example, with 

 the transfer of F? 



Fredericq: It is about of the same order. I made no comparative 

 control. It depends also on the type of colicin produced ; with some coli- 

 cinogenic strains between 10 and 80 per cent of the cells are transduced. 



Hayes: Do you have any colicinogenic strains whose capacity to pro- 

 duce colicin is not transferred at high frequency from an F+ to an F~ cell ? 



Fredericq: I have colicins which are not transferred at all. 



Hayes: Even when you select for a whole range of markers on that 

 part of the F+ chromosome which is only transferred at low frequency 

 in recombination? 



Fredericq: Yes, for example with the colicin produced by strain P9, it 

 seems that in the crosses there is induction of colicinogenic production 

 during transfer, and all recombinants which should receive the P9 

 property disappear. The number of recombinants is very low, not one is 

 colicinogenic, but the distribution of other markers among them is quite 

 normal. 



Hayes: In this case, if it had a locus on the chromosome one should 

 expect to find an elimination of a certain class of recombinants inheriting 

 markers which were linked to colicinogenicity. 



Fredericq: Yes, at least if it is linked with the markers. I have got no 

 indication that any colicinogenic properties are linked with any of the 

 markers. 



Hayes: The phenomenon of zygotic induction occurs in connexion with 

 the genetic transfer of X prophage and other inducible prophages in the 

 F"^ or Hfr parent, in a cross with a non-lysogenic F~ cell, but it seems 



