Identification of host receptor and receptor-binding module of a newly sequenced T5-like phage EPS7

The virulent bacteriophage EPS7 active against a number of Salmonella serovar and Escherichia coli strains, isolated from the local sewage in Korea, belongs to the family Siphoviridae. The ESP7 genome constitutes a linear double-stranded DNA of 111 382 bp. DNA sequencing and genomic analysis of EPS7 showed that it belongs to the phage T5 family. We identified the EPS7 genes involved in DNA repair, replication, viral structure and bacterial lysis by comparing the EPS7 genome with that of T5. In contrast, the tail genes encoding for putative host receptor-binding protein and the putative receptor-blocking lipoprotein precursor of EPS7 exhibit high homologies with the corresponding gene products of BF23, another member of the T5-family. BF23 binds to BtuB, a surface receptor in the host and involved in vitamin B12 uptake, but its infection is independent of TonB. By constructing a series of deletion mutants in Salmonella and in E. coli and studying phage infection in the mutant hosts, we showed that BtuB is also the host receptor of the phage EPS7. Whether EPS7 infection depends on TonB needs to be further studied.