The <i>tal</i> gene of lactococcal bacteriophage TP901-1 is involved in DNA release following host adsorption

Understanding the molecular mechanisms involved in phage-host interactions is essential to develop phage-based applications in the food and probiotic industries, yet also to reduce the risk of phage infections in fermentations. <i>Lactococcus</i>, extensively used in dairy fermentations, has been widely employed to unravel such interactions. Phage infection commences with the recognition of a suitable host followed by the release of its DNA into the bacterial cytoplasm. Details on this latter, irreversible step are still very scarce in lactococci and other Gram-positive bacteria. We demonstrate that a component of the baseplate of the lactococcal phage TP901-1, the tail-associated lysin (Tal), is involved in the DNA delivery into its host, <i>L. cremoris</i> 3107. Specifically, we have found that three amino acid changes in Tal appear to facilitate structural rearrangements in the baseplate necessary for the DNA release process, even in the absence of an otherwise required host trigger.