O antigen-dependent mutant of bacteriophage T5.

A T5 mutant is described which showed normal infection of Escherichia coli F but virtually no infection of cells lacking the E. coli F O antigen. This was due to very poor adsorption to the O antigen-deficient cells. Inactivation kinetics with anti-T5 serum and adsorption and desorption kinetics to receptor-deficient E. coli F cells suggested that the mutation did not affect the L-shaped tail fibers which mediate binding to the O antigen. Proof was obtained from genetic data; the structural gene for the L-shaped tail fibers mapped at a different position on the T5 chromosome than did the mutated gene. Since binding of the T5 mutant to the FhuA receptor protein was strongly inhibited by ferrichrome and since the mutation could not be crossed into phage BF23, we conclude that the mutation affects the receptor binding protein of the T5 tail.