COLICINS AND OTHER BACTERIOCINS 391 



substance, called pyocin, can be induced in the whole population 

 by exposure of the cultures to small doses of ultraviolet light or 

 other inducing agents. Pyocin is released into the medium by 

 bacterial lysis. It is adsorbed on specific receptors of susceptible 

 cells. Apparently a single particle of pyocin is suflftcient to kill 

 a cell (Jacob, 1954b). The pyocin released by P. pyocyanea PIO 

 behaves therefore in every respect as colicins do. The produc- 

 tion of such substances is not restricted to strain PIO. In the 

 course of a systematic investigation of various strains of P. 

 pyocyanea, Hamon (1956) found that about half of them produce 

 one or another pyocin active only on other strains of the same 

 species. Pyocins are protein-like substances that kill but are not 

 reproduced by sensitive cells. They are specifically adsorbed 

 by sensitive strains found only among Pseudomonas species. 

 They diff'er among themselves by such properties as host range, 

 diff'usion rate in agar, susceptibility to proteolytic enzymes, in- 

 ducibility etc. They are typical bacteriocins. 



In B. megaterium it was observed by Ivanovics and Alfoldi 

 (1954) that mutual antagonism between strains is a rather fre- 

 quent phenomenon attributable to the production of water- 

 soluble antibacterial substances, of a protein-like nature, called 

 megacins. As with other bacteriocins, the study of a particular 

 strain showed that exposure of the bacteria to ultraviolet light 

 induces biosynthesis of megacin which, after a latent period of 

 70 minutes, is released into the medium by lysis of the cells. 

 Efforts to detect phagelike particles in the lysate failed (Ivano- 

 vics and Alfoldi, 1955). 



A striking difference between a megacin and other bacterio- 

 cins was found by Ivanovics, Alfoldi, and Abraham (1955). 

 The range of action is much broader. Not only does this mega- 

 cin exert a lethal activity against every strain of B. megatherium 

 tested, but it is also active against other bacteria such as B. 

 sublilis, B. anthracis, and various pigment-forming cocci, such as 

 Micrococcus aurentiacus and M. cinnabareus. With some excep- 

 tions, sensitivity to this megacin appears to parallel susceptibility 

 to lysozyme (Ivanovics and Alfoldi, 1957). 



