Discussion 337 



it may not occur if the cross is made at temperatures much lower than 

 37°. In other words, 100 per cent zygotic induction only occurs when the 

 zygotes are made at 37°. Have you any information as to whether a 

 similar phenomenon arises in those strains where you get no transfer 

 of colicinogenicity ? At lower temperatures you might get segregation. 



Fredericq: This has not yet been done, but it should be investigated. 



Cavalli-Sforza: Have you tried to transduce colicin production by 

 phage ? 



Fredericq: I have tried this in some experiments, but without success. 

 It has not yet been done on a large scale. 



Poniecprvo: Is anything analogous to colicins found in other bacteria? 



Fredericq: There may, perhaps, be something analogous to colicins in 

 other bacteria. Jacob (1954, Ann. Inst. Pasteur, 86, 149) has studied 

 the production of pyocin by Pseudomonas, but so far transduction has 

 not been possible. In Hungary, Ivanovics and Alfoldi (Ivanovics, G., 

 and Alfoldi, L. (1954). Nature, Lond., 174, 465) studied the production 

 of megacine, an antibiotic whose synthesis is also induced by ultraviolet 

 irradiation, but so far there is no indication that the process may be 

 transduced from one strain to the other. 



Pollock: What is the situation with regard to the purification of colicins ? 



Fredericq: Colicin K has been purified recently by Goebel and his 

 collaborators at the Rockefeller Institute (Goebel et. ah, 1955, loc. cit.). 

 They obtained a very active product which seems to consist of a protein, 

 lipid and carbohydrate complex containing about 6 per cent nitrogen 

 and 1 • 6 per cent phosphorus. This compound seems to have all the 

 properties of the somatic antigen of the bacteria ; but these authors do 

 not exclude that colicin K may in reality be another molecule which is 

 linked with this complex. Colicins seem to be very high-molecular 

 compounds. Latarjet and I studied the X-ray inactivation curve of 

 colicin K, and the results point to a molecular w^eight between 60,000 

 and 90,000 (Latarjet and Fredericq, 1955, loc. cit.). 



Stocker: Prof. Fredericq, have you made any further observations on 

 the phenomenon you reported some years ago, i.e. the appearance of 

 minute clear areas, similar to phage plaques, produced by the action of 

 colicin-containing sterilized broth cultures on lawns of sensitive organ- 

 isms (Fredericq, P. (1950), C. R. Soc. Biol., Paris, 144, 728, 730)? That 

 seemed to suggest that there was some cell propagation of the active agent 

 under some circumstances, because it seems inconceivable that one 

 molecule could produce a visible area of clearing. 



Fredericq: This phenomenon which mimics phage tache is due to the 

 fact that in a colicinogenic culture not every cell produces colicin, and 

 the few which do produce colicin adsorb most of the colicin they produce ; 

 and when you put a drop of bacterial cultures on a sensitive indicator 

 those cells which have adsorbed a large quantity of colicin function as a 

 disseminating centre. As a rule, if you centrifuge then most of the tache- 

 producing activity is deposited. 



Hayes: Is there any analogue of recombination between two genetic 

 loci each of which determines a different type of colicin production ? 



Fredericq: I am now studying two strains which produce at the same 



