Receptors Determine Lytic Phage Host Range in Pseudomonas aeruginosa

As antimicrobial-resistant pathogens, particularly the rapidly mutating and adapting Pseudomonas aeruginosa , claim millions of lives worldwide each year, the development of novel therapeutic approaches becomes increasingly important. Bacteriophages (phages), viral predators of bacteria, represent a promising solution to fight bacterial infections. However, persistent challenges hinder the widespread application of phage therapy. One of these challenges is the narrow host range of bacteriophages, which are highly specific and only target a limited range of bacterial strains. This specificity poses difficulties in treating polymicrobial infections and limits broader application. Extensive research has been conducted to study host range, however, a definitive answer to the phage or bacterial factors determining phage host range remains elusive. In this work, we combined a transposon mutagenesis library and a Genome-Wide Association Study to identify bacterial genes associated with resistance or susceptibility to the lytic phages OMKO1 and LPS-5. We find that the flagellum is crucial for infection by phage OMKO1 and that lipopolysaccharide biosynthetic genes were significantly associated with LPS-5 phage susceptibility. These results suggest that these structures serve as receptors, which we confirmed through knockout swimming and LPS/O-antigen assays, respectively. Surprisingly, the presence of bacterial defense mechanisms was not a significant predictor of lytic phage infection but was for lysogenic phage infection. Together, these data indicate that receptor structures are important for phage infection. Conversely, they do not support existing paradigms regarding the central role of phage defense mechanisms in determining host range for lytic phages.