Adsorption of Bacteriophages to Homologous Bacteria 



The velocity of adsorption of phage to living bacteria was measured either di- 

 rectly, or by adding bacteriophages to a mixture of dead and living bacteria and 

 then determining their distribution over the two components. 



A 6-hour-old agar slant of coli 88 is suspended in broth and freed of larger 

 clumps by short centrif ugation ; half of this suspension is placed on ice, and the 

 other half is heated for 30 minutes in a water bath at 70°. The cell concentration 

 in each of the cultures is then determined by microscopic counts. 0.9 ml aliquots 

 of each culture, as well as equal volumes of a two-fold dilution, are placed in the 

 water bath at 37° and infected with 0.1 ml of a 1000-fold dilution of the phage 

 lysate. After 3 and 6 minutes, or after 6 and 12 mmutes, aliquots of each mixture 

 are diluted 10-fold and centrifuged at once at 8000 r.p.m. and the titer of the 

 supernatant liquid determined. The values of k, calculated from the experi- 

 mental results, are presented in Table II. (The uncentrifuged mixtures are also 

 titrated; in the experiment with living bacteria, the infective titer remains equal 

 to that of the original lysate ; whereas, in the experiment with dead bacteria, the 

 surviving infectivity is always equal to that of the infectivity of the supernatant 

 liquid.) 



The suspensions of living and dead bacteria are then mixed with one another 

 m the following proportions: 5 -f 5, 3 + 7, 2 + 8, and 1+9. To each of 

 0.9 ml of these mixtures, as well as to a suspension of only living bacteria, 0.1 ml 

 of the lysate dilution is added and an aliquot of 0. 1 ml of each mixture spread on 

 agar plates after 15 minutes. During this time no multiplication of the bacterio- 

 phage takes place, whereas most of the phages are already adsorbed. Since any 

 phage adsorbed to a living bacterium manifests itself by plaque formation, one 

 may infer that any observed decrease in phage titer must represent phages ad- 

 sorbed to dead bacteria. This decrease thus permits a calculation of the ratio of 

 the adsorption velocity constants k (living) k (dead) which apparently indicates 

 the distribution of phages over two competing components. The result of this 

 experiment is presented in Table III. 



Microscopic counts of the suspension of dead bacteria indicated a concen- 

 tration of 4.7 X 10^, of the suspension of living bacteria a count of 5.8 X lOVml. 

 These figures are reduced by 10% in the reaction mixture through dilution upon 

 addition of the phage lysate. 



The results of direct measurement of the adsorption velocity are presented in 

 Table II. 



Table II 



Thus, according to this experiment, with the ratio of the two velocity constants 

 being 2.6, the average value of k is 1.0 X 10~^^ for dead bacteria and 2.6 X 10~^^ 



29 



