High-resolution metagenomic characterization of gut microbiota composition and functional pathways in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder characterized by abdominal pain, altered bowel habits, and frequent comorbidity with anxiety and depression. The gut microbiota has been implicated in gut-brain axis (GBA) dysfunction, but consistent microbial signatures remain unclear. We performed whole metagenome shotgun sequencing of stool samples from 63 female patients with moderate to severe IBS and 34 female healthy controls and assessed microbial composition and functional pathways. Microbial richness and diversity were slightly reduced in IBS, though with high variability and no robust separation from controls. Differential abundance analyses revealed enrichment of Streptococcus sp. and the sulfate-reducing bacterium Desulfovibrio piger in IBS, alongside reductions in Bifidobacterium and Methanobrevibacter. Functional profiling identified 39 differentially abundant pathways: amino acid biosynthesis (e.g., L-isoleucine, L-threonine) was more prominent in IBS, while carbohydrate degradation pathways (e.g., galactose, stachyose) were enriched in healthy controls. These findings indicate modest but significant IBS-associated shifts in gut microbial composition and function that may contribute to IBS symptoms. However, high intra-group variability underscores the complexity of IBS and highlights the need for larger, multi-omics studies to define robust microbial markers. These results contribute to a growing body of evidence emphasizing the complexity of gut microbiota-host interactions and the need for high-resolution, systems-level approaches in microbiome-associated disorders.