ADSORPTION OF PHAGE TO HOST CELL 159 



sistance is marked by a change in the chemical constitution of the 

 polysaccharide moiety of the lipocarbohydrate-protcin antigen 

 of the organism. Whether changes occur also in Hpid or protein 

 portions is not known. 



The mechanism of phage inactivation by PIA is in most cases 

 unknown. However, Jesaitis and Goebel (1955) studied the 

 inactivation of phage T4 by the specific lipocarbohydrate which 

 had been isolated from the antigenic complex of phase II Sh. 

 sonnei. The addition of this lipocarbohydrate to a concen- 

 trated suspension of T4 phage results in an immediate large in- 

 crease in viscosity (see also Jesaitis and Goebel, 1953). Elec- 

 tron microscope examination reveals phage ghosts and long 

 filaments, probably of deoxyribonucleic acid (DNA). The 

 phage DNA is susceptible to degradation by deoxyribonuclease. 

 These results show that attachment of T4 to bacterial receptor 

 substance causes the release of DNA from the phage particles. 



Weidel and his collaborators studied receptor substance for T5, 

 isolated from E. coli B, with results paralleling those described 

 above in many respects (Weidel, Koch, and Bobosch, 1954; 

 Weidel and Koch, 1955; Weidel and Kellenberger, 1955; 

 Koch and Weidel, 1956a). 



6. Summary 



Adsorption is defined as attachment of the phage particle to 

 the host cell surface. The particles attach by the tips of their 

 tails. The kinetics of adsorption is that of a first-order reaction, 

 the rate being proportional to the varying phage concentration 

 and to the constant amount of bacterial surface. The adsorp- 

 tion rate is markedly aff'ected by environmental conditions such 

 as salt concentration, pH, and temperature. Some phages re- 

 quire the presence of organic molecules which must become fixed 

 to the phage before adsorption occurs. This cofactor require- 

 ment for adsorption is subject to modification by mutations of the 

 phage. Adsorption probably involves at least two successive 

 steps, the first of which is reversible. The rate of the first step is 

 little affected by temperature, whereas the rate of the second 



