Metagenomic analysis of vitamins B and K₂ biosynthesis by gut microbiota in wild birds

The role of gut microbiota in vitamin biosynthesis in wild birds, which is essential for understanding avian health and ecological adaptation, remains largely unexplored. In this study, metagenomic analysis was conducted on 10,455 metagenome-assembled genomes (MAGs) from 718 wild bird gut samples. After quality assessment and dereplication, 1947 MAGs were retained for systematic analysis of vitamin B and K₂ biosynthesis potential. A total of 106,336 vitamin biosynthesis genes were identified, and 1164 MAGs (including 410 high-quality MAGs with > 90% completeness and < 5% contamination) were predicted to de novo synthesize at least one vitamin. Vitamin biosynthesis genes mainly originated from Pseudomonadota, Campylobacterota, Bacillota_A, and Actinomycetota, with dominant genera including Campylobacter_D, Escherichia, and Cutibacterium. Compared with chickens, the gut microbiota of wild birds was enriched in biotin, folate, and pantothenate biosynthesis genes, likely reflecting adaptation to diverse natural diets and fluctuating environments. Among all examined factors, host species explained the largest proportion of variation in vitamin biosynthesis gene composition, followed by environmental variables, while migratory behavior and primary diet showed relatively smaller but detectable associations. Dietary differences appeared to be associated with variations in vitamin biosynthetic potential, with crop- and insect-dominant birds tending to show higher representation of genes involved in the synthesis of multiple B vitamins, whereas aquatic-plant dominant birds exhibited relatively greater representation of folate biosynthetic pathways. Migratory birds exhibited significantly higher diversity but comparable relative abundance of vitamin biosynthesis genes compared with resident birds, suggesting a more flexible microbial metabolic potential to meet fluctuating nutritional demands during long-distance movement. Distinct microbial contributors were identified, with Escherichia and Pseudomonas_E being more prominent in migratory birds, and Campylobacter_D in resident birds. Collectively, this study provides novel insights into gut microbiota-driven vitamin biosynthesis in wild birds.