232 



ZINDER AND LEDERBERG 



aliquots. Except for a small systematic 

 loss, probably mechanical, all units of 

 FA are accounted for either in the 

 supernatant or the sediment. 



The interference in adsorption im- 

 plied by saturation was demonstrated 

 more explicitly in a blocking experi- 

 ment. SW-188 (methionineless, M — ) 



32 r 



was exposed to an excess of FA from 

 M— cells for fifteen minutes. FA from 

 LT-7 (M-I-) was then added to the 

 sedimented cells for an additional fif- 

 teen minutes before the cells were 

 again sedimented. The M+ FA was 

 not bound, nor was the SW-188 trans- 

 duced. This verifies the blocking con- 



28 



24 



20 



16 



LEGEND 

 0--0 SEDIMENT 

 X — X SUPERNATANT 



TOTAL RECOVERY 



INPUT 



4 - 



Fig. 6. Adsorption of FA. IQi"^ cells of LA-22 were exposed to FA (LT-2) for 15 

 to 30 minutes. Supernatants and sediments were collected after centrifugation and 

 assayed, respectively, for residual FA and for transductions already initiated. 



cept and indicates that the adsorption 

 is irreversible after the fifteen minutes 

 allowed for saturation. 



Since adsorption of FA is so rapid 

 it appears safe to assume that the large 

 proportion of the individual bacteria 

 are capable of adsorbing it. We can 

 make an approximate minimum esti- 

 mate of the number of adsorbable par- 

 ticles per ml of this filtrate by dividing" 

 the total number of bacteria by the 

 number of ml required to saturate 

 them (one particle per bacterium); 



lO^VS or 1.3 X 10*'. A maximum num- 

 ber of particles per ml is set by the fact 

 that the active filtrate showed no tur- 

 biditv" as might be expected with more 

 than 10^^ particles per ml. 



So many unverified postulates are 

 required that a detailed discussion of 

 possible models for the kinetics of 

 adsorption would be unprofitable here. 

 It may be pointed out, however, that 

 the low or zero frequency of double 

 exchanges does not imply that one 

 species of FA particle excludes an- 



