A Lactococcal Phage Protein Promotes Viral Propagation and Alters the Host Proteomic Response During Infection

The lactococcal virulent phage p2 is a model for studying the genus, the most prevalent group of phages causing milk fermentation failures in cheese factories worldwide. This siphophage infects MG1363, a model strain used to study Gram-positive lactic acid bacteria. The structural proteins of phage p2 have been thoroughly described, while most of its non-structural proteins remain uncharacterized. Here, we developed an integrative approach, making use of structural biology, genomics, physiology, and proteomics to provide insights into the function of ORF47, the most conserved non-structural protein of unknown function among the genus. This small phage protein, which is composed of three α-helices, was found to have a major impact on the bacterial proteome during phage infection and to significantly reduce the emergence of bacteriophage-insensitive mutants.