Adsorption of Bacteriophages to Homologous Bacteria 



heat-killed bacteria, whose 2.6-fold reduction in adsorption velocity possibly 

 reflects in inactivation of the phage receptors of a corresponding fraction of the 

 cell surface, then one might revise this estimate of the phage diameter down to 

 values of 61 to 120 m/x. 



Thus, two completely independent sets of data, the adsorption velocity and the 

 saturation capacity, yield roughly the same value for the diameter of the bacterio- 

 phage: 100 mM and 60-120 m^ respectively. These figures appear much too high 

 when compared with most of the values for the particle diameter given in the 

 hterature. In recent months, however, we have succeeded in measuring the 

 sedimentation velocity in a centrifuge run at 7000 to 8000 r.p.m., of phage 

 particles from lysates of the same coli phage selected for the present adsorption 

 experiments. These measurements, which no doubt exceed all others in reliabil- 

 ity, allowed us to calculate a particle size of 80 to 90 m/u. By means of a successive 

 series of repetitive centrifugations, we were finally able to sediment into a pellet 

 up to 99.99% of the active particles without encountering any decrease in the 

 sedimentation velocity, i.e., without detecting any particles of smaller diameter, i" 



The agreement of the values of the phage diameter calculated indirectly from 

 the adsorption velocity and from the saturation capacity, and the similarity of 

 these values to the phage diameter determined directly, substantiates the validity 

 of our assumptions. In any case, the formal kinetics of the process as well as the 

 actual numerical values of the relevant parameters can be integrated, without 

 contradiction, into the following simple picture. In each suspension of a mixture 

 of bacteria and bacteriophages collisions occur between the individual particles of 

 the two components. These collisions are entirely random, and their frequency is 

 mainly determined by the Brownian movement of the bacteriophages. In the 

 case of bacteriophage particles of maximum adsorption aflfinity (and in our coli 

 lysate most of the particles are of this nature), the first such random collision 

 between phage and bacterial cell leads to an irreversible fixation. More precisely, 

 in the case of young, living bacteria almost every collision leads to fixation and in 

 the case of heat-killed bacteria approximately every third collision does ' ^ In the 

 case of phage particles of reduced affinity, only a fraction of the collisions leads to 

 fixation; and here also the fixation is less stable and partially reversible. The 

 bacteria conserve their ability to find additional bacteriophage particles as long as 

 their surfaces are not completely covered by a monolayer of such particles. 

 Investigations on the influence of the medium on the absorption process shall be 

 communicated in a future paper. 



Summary 



1 . The equation describing the adsorption kinetics derived in a previous paper 



2.3 log - = kht 



rit 



i^The results of this investigation will be published in this journal. 



i^This statement refers only to the experimental conditions communicated here, that is to 

 say, to a broth medium and to the temperature of the incubator. 



35 



