Characterization of the Distal Tail Fiber Locus and Determination of the Receptor for Phage AR1, Which Specifically Infects Escherichia coli O157:H7

Abstract

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 does 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 totally 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 not between AR1 and T4. The sequences that are most closely related to the AR1 gp37 and gp38 are those of phage Ac3 in the T2 family. To identify the AR1-specific receptor, E. coli O157:H7 was mutated by Tn10 insertion and selected for an AR1-resistant phenotype. A mutant so obtained has an insertion occurring at ompC that encodes an outer membrane porin. To confirm the role of OmpC in the AR1 infection, homologous replacement was used to create an ompC disruption mutant (RM). When RM was complemented with OmpC originated from an O157:H7 strain, but not from K-12, its AR1 susceptibility was fully restored. Our results suggest that the host specificity of AR1 is mediated at least in part through the OmpC molecule.

Genes under positive selection in Escherichia coli

“…OmpC has been reported to play a key role in virulence of Salmonella (Negm and Pistole 1999), and it also functions as the receptor for several phages. A major varied segment between residues176 and 226 has been reported to affect phage infectivity (Tommassen et al 1985;Mizuno et al 1987;Hikita et al 1989;Yu et al 2000). We found evidence of positive selection in residues 163, 202, and 203, located on loops 4 and 5, suggesting that the positive selection acting on ompC is selection to avoid phage binding, but selection to enhance OmpC's function as a virulence factor may also be important.…”

T4-Like Genome Organization of the Escherichia coli O157:H7 Lytic Phage AR1

“…In previous studies, partial sequences of AR1 showed a high degree of similarity to the corresponding sequences of T4 phage (17,37,89,90). In this study, we determined the complete genome sequence of AR1 (167,435 bp).…”

“…Host range receptor assays (17) showed that AR1 uses the R1, R3, and R4 core oligosaccharide (OS) types of lipopolysaccharide (LPS), but not the R2 or K-12 type, as cellular receptors (17). A previous study suggested that the putative AR1 gp37 receptor recognition protein may recognize and bind to the OmpC receptor because an E. coli O157:H7 OmpC disruption mutation rendered the cell resistant to AR1 infection (90). Similar to the case with T4 and other T4-like phages, restric-tion enzyme digestion experiments suggested that the AR1 genome is highly modified to protect it from restriction enzyme digestion by the host defense system (89).…”

Structure of the receptor-binding carboxy-terminal domain of bacteriophage T7 tail fibers

“…Only a few phages appear to have evolved by mutation maintaining the same structural framework. Residues 359-524 of T7 gp17 (encompassing all but the final 29 residues of our structure) have been classified in Pfam domain gp37_C, which includes a subset of the highly diverged Cterminal regions of the gp37-type tail-fiber proteins of T4-like phages, the subset found in phages AR1 and Ac3 (30). Thus, amino acid sequence comparisons suggest that the tapered triangular pyramid and part of the tip structure of T7 tail fibers may be structural building blocks used in fibers of phages of the Myoviridae as well as the Podoviridae family.…”