Structural and functional characterization of the receptor binding proteins of O157 phages EP75 and EP335.

Bacteriophages (phages) are widely used as biocontrol agents in food and as antibacterial agents for treatment of food production plant surfaces. An important feature of such phages is broad infectivity towards a given pathogenic species. Phages attach to the surfaces of bacterial cells using receptor binding proteins (RBPs), namely tail fibers or tailspikes (TSPs). The binding range of RBPs is the primary determinant of phage host range and infectivity, and therefore dictates a phage's suitability as an antibacterial agent. Phages EP75 and EP335 broadly infect strains of serotype O157. To better understand host recognition by both phages, here we focused on characterizing the structures and functions of their RBPs. We identified two distinct tail fibers in the genome of the podovirus EP335: gp12 and gp13. Using fluorescence microscopy, we reveal how gp13 recognizes strains of serotypes O157 and O26. Phage EP75 belongs to the genus within the family and features a four TSP complex (TSPs 1-4) that is universal among such phages. We demonstrate enzymatic activity of TSP1 (gp167) and TSP2 (gp168) toward the O18A and O157 O-antigens of respectively, as well as TSP3 activity (gp169.1) against O4, O7, and O9 O-antigens. TSPs of EP75 present high similarity to TSPs from phages CBA120 (TSP2) and HK620 (TSP1) and myovirus Det7 (TSP3), which helps explain the cross-genus infectivity observed for EP75.