Listeria phage A511, a model for the contractile tail machineries of SPO1-related bacteriophages.

Recognition of the bacterial host and attachment to its surface are two critical steps in phage infection. Here we report the identification of Gp108 as the host receptor-binding protein of the broad host-range, virulent Listeria phage A511. The ligands for Gp108 were found to be N-acetylglucosamine and rhamnose substituents of the wall teichoic acids of the bacterial cell wall. Transmission electron microscopy and immunogold-labelling allowed us to create a model of the A511 baseplate in which Gp108 forms emanating short tail fibres. Data obtained for related phages, such as Staphylococcus phages ISP and Twort, demonstrate the evolutionary conservation of baseplate components and receptor-binding proteins within the Spounavirinae subfamily, and contractile tail machineries in general. Our data reveal key elements in the infection process of large phages infecting Gram-positive bacteria and generate insights into the complex adsorption process of phage A511 to its bacterial host.