ADSORPTION OF PHAGE TO HOST CELL 143 



could not be a step in the infective process (Hershey, personal 

 communication). Further work described below has led to the 

 contrary interpretation. 



There were no further quantitative studies of the effect of salts 

 on phage adsorption until the work of Puck, Garen, and Cline 

 (1951). These authors studied the rates of adsorption of various 

 phages to E. coli under a variety of environmental conditions, 

 and reached the conclusion that the initial step in phage adsorp- 

 tion is the establishment of electrostatic bonds between appro- 

 priate configurations of ionic charges on the two bodies. 



In these studies the first-order velocity constants are used to 

 characterize the adsorption rates as the environmental conditions 

 are changed. With phage Tl in buffered salt solutions at 37 ° G. 

 the optimum salt concentration for phage adsorption is about 

 0.01 M for salts of univalent cations and 0.001 M for salts of 

 divalent cations. The rate of adsorption is depressed markedly 

 by higher or lower concentrations. The maximum velocity 

 constant is the same in simple salt solutions and in broth, sug- 

 gesting that no cofactors other than salts are required. Puck, 

 Garen, and Gline (1951) adopted the hypothesis, consistent with 

 their results, that the efficiency with which collisions between 

 phage particles and cells lead to attachment is controlled by 

 electrostatic charges on the colliding bodies, and that cations in 

 the medium afTect adsorption bv influencing these charges. 



3. Organic Cofactors 



T. F. Anderson (1945a) discovered that some phages are un- 

 able to adsorb to their host cells unless certain organic compounds 

 are present in the environment. He compared plaque counts of 

 phage stocks on the usual nutrient broth agar with counts on 

 agar prepared from ammonium lactate and other salts. Coli- 

 phage T2 gives the same counts on the two media, whereas 

 counts of T4 and T6 are much lower on lactate agar than on 

 broth agar. By testing various substances that might be present 

 in broth he found that the addition of tryptophan or phenyl- 

 anlaine to the svnthetic medium results in a large increase in the 



