A FhuA mutant of Escherichia coli is infected by phage T1-independent of TonB

Infection of Escherichia coli K-12 by phages T1 and φ80 requires the FhuA outer membrane protein and the TonB protein. Mutations in the N-terminal globular domain close to the predicted channel in the β-barrel of FhuA were created. The FhuAΔ107–111 N104K K110D L111P mutant and the FhuA(L109DPNGLK110) insertion mutant were sensitive to phage T1, but nearly resistant to phage φ80. FhuAΔ107–111 N104K K110D L111P mediated phage T1 infection in a tonB mutant without formation of TonB-independent phage T1 host-range mutants. The FhuA mutants showed no altered sensitivity to phage T5. Although the phages share overlapping binding sites in FhuA, the structural alterations elicited by the mutations resulted in very different phage sensitivities. In the FhuA deletion mutant, the TonB requirement for phage T1 infection was partially bypassed.