384 BACTERIOPHAGES 



c. Physicochemical Properties 



Although they differ in many of their properties, many coHcins 

 are rapidly destroyed by proteolytic enzymes (Frcdericq, 1948), 

 and were assumed to be proteins. More recent observations, 

 however, indicate that they may be more complex, perhaps lipo- 

 carbohydrate proteins (Goebel, Barry, Jesaitis, and Miller, 

 1955). Little work has been done on the properties and nature 

 of colicins. Fredericq has shown that the different colicins vary 

 widely in properties such as diffusibility, or sensitivity to heat and 

 pH. Different colicins seem to differ in size. For instance 

 colicin V of Gratia forms a very wide zone of inhibition on agar 

 (2 to 3 cm. in diameter) and diffuses through cellophane mem- 

 branes, whereas a colicin of type A gives a narrow halo of inhi- 

 bition and is not dialyzable (Fredericq, 1948). A few colicins 

 have been studied in more detail : one of type V by Heatley and 

 Florey (1946), several of the V and D type by Gardner (1950), 

 and one of type E from E. coli ML by Jacob, Siminovitch, and 

 Wollman (1952), These colicins, very soluble in water, are pre- 

 cipitated by ammonium sulfate and organic solvents. Even the 

 large colicins, such as that produced by E. coli ML, are not sedi- 

 mented by centrifugation at 20,000 X g for two hours. They 

 are insensitive to ultraviolet light and to ribo- and deoxyribonu- 

 clease. 



A more detailed analysis of a colicin K was undertaken by 

 Goebel, Barry, and Shedlovsky (1956). They prepared large 

 quantities of this colicin and concentrated and purified it by re- 

 peated precipitations with 75 per cent ethanol at ° C. and with 

 75 per cent ammonium sulfate at pH 4.5, followed by dialysis 

 and treatment with chloroform-octyl alcohol. The material 

 thus obtained is thermostable. A spot test with 0.02 jug com- 

 pletely inhibits the growth on agar of sensitive bacteria. Con- 

 trary to what had been reported for other colicins, colicin K is a 

 potent antigen. Antiserum prepared against it agglutinates the 

 bacteria that produce it. In its chemical, physical, immunolog- 

 ical, and toxic properties, colicin K appears to be very similar to 



