Abstact

Bacteriophages play crucial roles in modulating the human gut microbiome, yet structural characterization of prevalent gut phages remains limited. Here, we present high-resolution cryo-EM structures of Parabacteroides phage PD491P1, which is one of the most abundant bacteriophages in the human gut. The structures reveal its mature virion organization, including the capsid, head-to-tail interface, and tail tip regions. Strikingly, PD491P1 exhibits an exceptionally extensive disulfide bond network that covalently stabilizes nearly the entire virion. Unique structural features include an elaborate portal-adaptor-terminator interface and distinctive, upward-pointing and flexible tail fibers with multiple putative host recognition domains. These structural adaptations may enable phage PD491P1 to achieve survival and robust infection in the challenging gut environment. These findings expand our understanding of gut phage structural diversity, reveal mechanistic insights into phage stability and infection, and provide a foundation for future development of phage-based microbiome therapeutics.