Identification and characterization of novel outer membrane proteins of Brachyspira pilosicoli

Brachyspira pilosicoli is a globally prevalent, anaerobic, Gram-negative spirochete that causes intestinal spirochetosis in birds, pigs, and humans. It colonizes the large intestine, causing colitis, diarrhea, and impaired growth. Despite its pathogenic relevance, the outer membrane proteins of B. pilosicoli remain largely uncharacterized. In this study, we computationally identified a total of 42 outer membrane β-barrel (OMBB) proteins within the B. pilosicoli proteome using a consensus-based computational framework. Structural models generated using AlphaFold 3 confirmed the β-barrel architectures of the predicted proteins. Structure- and sequence-based functional annotations revealed homologs of b-barrel assembly machinery BamA protein, lipopolysaccharide-assembly protein LPS-assembly protein D, TolC, transporter proteins, enzymes, diffusion channels, and porins. Notably, seven of the predicted OMBB proteins were previously unannotated in UniProt and the National Center for Biotechnology Information; we report their putative functions here for the 1st time. Sequence variation analysis among the homologs of OMBB proteins across nine B. pilosicoli strains revealed that many of the variations were present within surface-exposed loop regions, suggesting roles in host interaction and immune modulation. Our in silico study expands the functional repertoire of B. pilosicoli outer membrane proteins, highlighting potential targets for diagnostics, vaccine development, and therapeutic interventions.