Molecular basis of Gram-positive host recognition by the Oenococcus oeni phage OE33PA

Bacteriophages (phages) infecting Gram-positive bacteria must bind to host receptors across thick cell walls to initiate infection, yet the underlying structural mechanisms remain unclear. Here, we report cryo-electron microscopy structures of the Oenococcus oeni siphophage OE33PA, providing the first atomic resolution view of a phage infecting this bacterium important for the wine industry. While the overall virion architecture is conserved, the adhesion device displays distinctive features. Its receptor-binding proteins adopt multiple orientations, revealing an intrinsically dynamic assembly. In situ cryo-electron tomography captures distinct conformations upon host attachment, providing rare structural insight into interactions with Gram-positive hosts. Additionally, functional assays show that a highly mobile carbohydrate-binding module in the distal tail protein mediates host-specific binding. Furthermore, the tape measure protein, central to phage assembly and infectivity, adopts a hexameric organization, updating the prevailing trimeric model in siphophages. Together, these findings reveal a dynamic adhesion device in a phage infecting Gram-positive bacteria and highlight the structural and functional diversity of phages.