Characterization of the distal tail fiber locus and determination of the receptor for phage AR1, which specifically infects Escherichia coli O157 : H7

Phage AR1 is similar to phage T4 in several essential genes but differs in host range. AR1 infects various isolates of Escherichia coli O157:H7 but do es not infect K-12 strains that are commonly infected by T4. We report here the determinants that confer this infection specificity. In T-even phages, gp37 and gp38 are components of the tail fiber that are critical for phage -host interaction. The counterparts in AR1 may be similarly important and, therefore, were characterized. The AR1 gp37 has a sequence that differs tot ally from those of T2 and T4, except for a short stretch at the N terminus. The gp38 sequence, however, has some conservation between AR1 and T2 but n ot between AR1 and T4. The sequences that are most closely related to the A R1 gp37 and gp38 are those of phage Ac3 in the T2 family. To identify the A R1-specific receptor, E. coli O157:H7 was mutated by Tn10 insertion and sel ected for an AR1-resistant phenotype. A mutant so obtained has an insertion occurring at ompC that encodes an outer membrane porin. To confirm the rol e of OmpC in the AR1 infection, homologous replacement was used to create a n ompC disruption mutant (RM). When RM was complemented with OmpC originate d from an O157:H7 strain, but not from K-12, its AR1 susceptibility was ful ly restored. Our results suggest that the host specificity of AR1 is mediat ed at least in part through the OmpC molecule.