Role of the bacteriophage P22 tail in the early stages of infection.

The initial binding of phage P22 to its host, Salmonella typhimurium, is dependent in a linear fashion on the number of tail parts per phage head. (The normal head has six.) There is also a later step which depends on tail parts. This step must occur some time after hydrolysis of the O antigen has been initiated and before ejection of phage DNA from the head is complete. This step causes PFU to depend on approximately the third power of the number of tail parts per head.