Methanogens as hidden architects of intestinal ecology in monogastric animals: distribution and function

Methanogens, strictly anaerobic archaea within the gut microbiota of monogastric animals, play dualistic roles in host health through their unique molecular and metabolic characteristics. Distinguished by conserved 16S rRNA sequences, ether-linked membrane lipids, and archaea-specific cofactors (e.g., Coenzymes M and F₄₂₀), these microorganisms drive methanogenesis via hydrogenotrophic, aceticlastic, and methylotrophic pathways. Despite their low abundance (~1%–10% of gut anaerobes), methanogens critically regulate the host's metabolic homeostasis by scavenging hydrogen to enhance fibrolytic bacterial activity, improving dietary fiber degradation and nutrient absorption. However, their overgrowth correlates with metabolic disorders such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), obesity, and chronic constipation, underscoring a functional duality. Host-specific distribution patterns reveal the dominance of Methanobrevibacter smithii in humans and pigs, while Methanomassiliicoccales and Methanosphaera occupy niche roles in rabbits and companion animals. Their abundance is shaped by developmental stages (e.g., maternal transmission, post-weaning shifts), dietary fiber intake, physiological states (e.g., IBD-linked reduction, IBS/obesity-associated proliferation), and environmental stressors (e.g., ammonia tolerance). Current research limitations include bacterial-centric biases, undefined pathogenic thresholds, and scarce cross-species comparisons. Future directions emphasize multi-omics integration to elucidate methanogen–host interactions, develop 'archaebiotics' for targeted population modulation, and engineer ecological strategies (e.g., enhancing hydrogen sinks) to mitigate methane-related disorders. Advancing this knowledge will optimize therapeutic interventions for metabolic diseases, improve nutrient utilization, and reduce environmental methane emissions.