390 BACTERIOPHAGES 



transferred with different frequencies, sometimes very high 

 (Frcdericq, 1954a). 



Transfer of coHcinogeny appears to be a consequence of bac- 

 terial conjugation. In crosses between noncolicinogenic and coli- 

 cinogenic bacteria, the colicinogenic character but not the non- 

 colicinogenic character can be transferred from the donor parent 

 to recombinants. The resulting asymmetry in reciprocal crosses 

 led Fredericq (Fredericq, 1954a, 1955; Fredericq and Betz- 

 Bareau, 1953) to postulate that colicinogeny is under the con- 

 trol of cytoplasmic determinants whose transfer requires di- 

 rect contact between bacteria of opposite mating types. 



Immunity to colicins associated with colicinogeny is distinct 

 from the resistance observed in mutants obtained by selection. 

 For instance, whereas mutants resistant to a given colicin of 

 group E are resistant to all the colicins of that group, bacteria 

 that produce a given colicin of group E may be sensitive to other 

 colicins of the same group. The immunity of colicinogenic bac- 

 teria, however, is neither as invariable nor as complete as the 

 immunity of lysogenic bacteria. A striking exception was de- 

 scribed by Ryan, Fried, and Mukai (1955). A strain of E. coli 

 that does not produce colicin under ordinary conditions of 

 growth releases, after exposure to ultraviolet light, a colicin ac- 

 tive on the producing strain. 



The transfer of colicinogeny in bacterial crosses enabled 

 Fredericq (1956) to analyze the immunity pattern of the resulting 

 colicin-producing derivatives. Most of these, although immune 

 to the concentration of colicin they produce, proved to be sensi- 

 tive to higher concentrations. The genetic relation between 

 the ability to produce a given colicin and immunity to its action 

 seems to be complex. 



4. Other Bacteriocins 



Strains of Psendomonas pyocyanea are known to produce antibi- 

 otic substances active on a wide variety of microorganisms. In 

 filtrates of a certain strain PIO one finds a substance acting only 

 on some other strains of the same species. The synthesis of this 



