Abstract
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 E. coli 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 E. coli serotypes O157 and O26. Phage EP75 belongs to the Kuttervirus genus within the Ackermannviridae 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 E. coli, respectively, as well as TSP3 activity (gp169.1) against O4, O7, and O9 Salmonella O-antigens. TSPs of EP75 present high similarity to TSPs from E. coli phages CBA120 (TSP2) and HK620 (TSP1) and Salmonella myovirus Det7 (TSP3), which helps explain the cross-genus infectivity observed for EP75.
Highlights
Despite the strict hygiene standards applied during food production and processing in the Western world, foodborne diseases remain a considerable burden on global human health [1,2]
TSPs of EP75 present high similarity to TSPs from E. coli phages CBA120 (TSP2) and HK620 (TSP1) and Salmonella myovirus Det7 (TSP3), which helps explain the cross-genus infectivity observed for EP75
The C-terminal 114 residues of gp13 were predicted to form an intramolecular chaperone domain (IMC), which assist with the folding and maturation of phage receptor binding proteins (RBPs) before autoproteolytic removal, as described for the long tail fiber of phage S16 (PDB ID: 6F45) [48], the TSP of phage K1F (PDB ID: 3GW6) [49], and the Bacillus phage GA-1 neck appendage (PDB ID: 3GUD) [49]
Summary
Despite the strict hygiene standards applied during food production and processing in the Western world, foodborne diseases remain a considerable burden on global human health [1,2]. In the US alone, around 48 million people acquire a foodborne illness annually resulting in 128,000 hospitalizations and 3,000 deaths [3]. A STEC infection results in common gastroenteritis and can lead to the development of life-threatening hemolytic uremic syndrome (HUS) [8]. Data obtained in 2019 by the Foodborne Diseases Active Surveillance Network (FoodNet) showed that the incidence of laboratory-diagnosed STEC infections in the US continues to rise. This implies a lack of progress in the global control of STEC contaminations during food production, and calls for the implementation of new biocontrol strategies
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