Phage Adsorption and Localization of Receptor Sites

Bacteriophage adsorption is one of those functions of the cell surface that has played a major role in the exploration of the composition of the 

Most cell-surface structures and organelles of gram-negative bacteria can serve as receptors for phage. Some of these are briefly reviewed here. 

In addition to the F-pili, which have already been discussed, phage can also adsorb to I-pili. 

Two sets of conditions were used to study phage adsorption (a) The cells were plasmolyzed in sucrose before addition of the phage, (b) The cells and phage were mixed before plasmolysis. Subsequent to adsorption (1-4 min at 37°C), the mixtures were diluted in the same medium, cells were sedimented by low-speed centrifugation, and fixed as described in Section 3.3. The supernatants were tested for phage titers in order to ascertain the extent of adsorption. 

In T-even phages, as well as in other phage systems, infection is assumed to involve a multiple sequence of steps. Following collision of the phage with the host, the adsorbed particle is still detachable and can be shown to retain its infectivity. This initial adsorption is followed by irreversible events, which include contraction of the tail sheath and exposure of the tail core through which the DNA will be extruded from the head into the host cell. 

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