Lactococcal phages Tuc2009 and TP901-1 possess a conserved tail fibre, called a Tail-Associated Lysin (referred to as Tal2009 for Tuc2009, and Tal901-1 for TP901-1), suspended from their tail tips that projects a Peptidoglycan-Hydrolase (PGH) domain towards a potential host bacterium. Tal2009 and Tal901-1 can undergo proteolytic processing mid-protein at the glycine-rich sequence GG(S/N)SGGG, removing their C-terminal structural lysin. In this study, we show that the PGH of these Tal proteins is an M23 peptidase which exhibits D-Ala-D-Asp endopeptidase activity, and that this activity is required for efficient infection of stationary phase cells. Interestingly, the observed proteolytic processing of Tal2009 and Tal901-1 facilitates increased host adsorption efficiencies of the resulting phages. This represents, to the best of our knowledge, the first example of tail fibre proteolytic processing that results in a heterogeneous population of two phage types. Phages which possess a full-length tail fibre, or a truncated derivative, are better adapted to efficiently infect cells with extensively cross-linked cell wall, or infect with increased host-adsorption efficiencies, respectively.
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