Metagenomic analysis of bile acid biotransformation by gut microbiota in wild birds

Although gut microbiota-mediated bile acid (BA) metabolism is well characterized in mammals, its mechanisms in wild birds remain largely unknown, hindering our understanding of their ecological adaptation and health. In this study, metagenomic analysis was performed on 10,455 metagenome-assembled genomes (MAGs) derived from 718 wild bird gut samples, from which 1,034 high-quality non-redundant MAGs were selected for further analysis. Functional annotation analysis identified 755 MAGs encoding genes associated with BA biotransformation pathways, primarily derived from the phyla Bacillota_A, Bacteroidota, and Bacillota, with dominant genera including Helicobacter_G and Ligilactobacillus. Subsequent genomic analysis identified 379 MAGs encoding bile salt hydrolase (BSH), with phylogenetic classification demonstrating predominant affiliation to the Bacteroidota and Bacillota_A phyla. Compared to the BSH-producing microbiota in the human and chicken gut, the phylum Bacillota exhibited a notably higher relative abundance in wild birds. Within the wild bird gut microbiome, Helicobacter_G was identified as the predominant BSH-encoding genus, whereas its relative abundance was substantially lower in both humans and chickens. Moreover, migratory birds (MB) displayed significantly higher diversity of BA biotransformation genes than resident birds (RB), with Helicobacter_G being notably enriched at the genus level in MB, potentially associated with their heightened energy and nutritional demands during migration. Notably, in addition to residency status, host species emerged as the most influential factor shaping the compositional variation of BA biotransformation genes, followed by environmental factors and dietary habits. In summary, this study systematically elucidates the potential functions of gut microbiota in BA metabolism and their close associations with host ecological traits in wild birds, not only advancing our understanding of host-microbe interactions and metabolic adaptation mechanisms but also providing a theoretical foundation for future interventions targeting gut microbiota to improve wildlife health.