Characterisation of new environmental bacteriophages targeting the Escherichia coli LamB outer membrane porin

Bacteriophages are viral parasites of bacteria. A successful infection starts with the adsorption of the bacteriophage to a specific receptor on the host cell surface. Most bacteriophages are thought to have a narrow host range but this can be extended in certain cases. One strategy forextending host range is to first express a known functional bacteriophage receptor protein in bacteria previously non-susceptible to the bacteriophage, thereby enabling adsorption and potential infection by viruses that target the specific receptor. To investigate the feasibility of this approach, a plasmid (pMUT13) encoding the Escherichia coli LamB porin, the receptor for bacteriophage Lambda, was transferred into three different enterobacterial genera, namely Citrobacter, Yersinia, and Serratia. Over 100 environmental bacteriophages were isolated that infected these pMUT13-containing strains, and some bacteriophages were shown to infect their respective hosts in a LamB-dependent way. The host ranges of the environmental bacteriophages were cross-tested across the heterologous genera and surface adsorption kinetics investigated. Unlike bacteriophage Lambda, which is a member of the Siphoviridae, these newly-isolated LamB-dependent bacteriophages were more commonly members of the Myoviridae, based on transmission electron microscopy and whole genome sequences. Furthermore, an interesting selection of evolved bacteriophage mutants with broader host range were isolated, and the key mutations involved in their evolution to adapt to new hosts were investigated by genome analysis.