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DISCUSSION 



Hayes: I should like to congratulate Prof. Fredericq on talking about 

 a true antibiotic and not one of these synthetic chemical compounds! 

 Prof. Fredericq has implied that the potentiality to produce colicin is 

 not a genie but a cytoplasmic factor because of the apparent maternal 

 inheritance of this potentiality since, when a donor strain unable to 

 produce colicin is crossed with a colicinogenic recipient strain, then all 

 the progeny are colicin-producers ; but when he does the reverse cross, i.e. 

 when the donor is colicinogenic and the recipient non-colicinogenic, then 

 there is segregation of colicinogenicity and non-colicinogenicity among 

 the progeny. What are the details of this reverse cross? Is it a true 

 reverse cross in that the same donor and recipient strains are used, but 

 simply the capacity or incapacity to produce colicin has been reversed? 



Fredericq: Yes, this was confirmed in many other types of crosses 

 where different markers were selected. When it is the reverse cross, it is 

 obvious; and when you make it with many different selected markers 

 and always get the same results, I think that is also quite demonstrative. 

 In the classical cross M— (F+) x TLBi-(F~) you can make the F+ or 

 the F~ parent colicinogenic. If it is the F~ which is colicinogenic, 100 

 per cent of the recombinants will be colicinogenic; but if it is the F+ 

 which is colicinogenic, then up to 60 or 70 per cent of the recombinants 

 may still be colicinogenic. 



Hayes: Can you transfer colicinogenicity to the F~ parent without 

 infecting it with F+? 



Fredericq: Transduction of the colicinogenic property very often 

 results in the simultaneous transduction of the F+ agent, but some 



