Elucidating key steps and players in the adsorption of DEV phage to its Pseudomonas aeruginosa host

Phage therapy is experiencing a resurgence of interest as a promising therapy for curing multidrug-resistant bacterial infections, although its clinical application remains limited and largely experimental. One significant challenge hindering phage therapy development lies in the modest knowledge of the biology of the bacteriophages employed, which limits the rational selection and engineering of phages for therapeutic applications. We have characterized the adsorption strategy of DEV, a component of a therapeutic phage cocktail able to cure Pseudomonas aeruginosa infections in different animal models. DEV is a podovirus belonging to the Schitoviridae family, whose first isolated member is the N4 phage of Escherichia coli. DEV uses the O-antigen moiety of lipopolysaccharide (LPS) as its primary receptor, recognized by the long tail fiber protein gp53. Notably, DEV can also infect deep-rough P. aeruginosa strains that produce truncated LPS lacking the O-antigen, suggesting the use of an alternative receptor. Our data point to the essential outer membrane protein LptD as this secondary receptor, with the receptor-binding protein (RBP) gp54 mediating the interaction. gp54 is encoded within the essential gp56–gp55–gp54 operon, where gp56 codes for a tail sealing short fiber. Intriguingly, DEV and N4 both exploit a surface glycan and the corresponding transporter for host recognition and their RBPs share structural similarity. To our knowledge, this represents the first report of a P. aeruginosa phage utilizing the essential outer membrane protein LptD as a receptor.