Regional Differences in Colonic Mucosal Temperature and Their Association with Gut Microbiota in Ulcerative Colitis

The human large intestine harbors a dense and regionally heterogeneous microbiota that plays a critical role in host physiology and disease.Because bacterial species exhibit distinct optimal growth temperatures, colonic mucosal temperature may influence gut microbial composition and mucosal immune responses.However, region-specific measurements of colonic mucosal temperature and their relationship with the intestinal microbiota, particularly in ulcerative colitis (UC), remain poorly understood.In this prospective single-center study, 25 patients with UC undergoing total colonoscopy were enrolled.Mucosal temperatures of the cecum and rectum were measured endoscopically, and axillary temperature was recorded simultaneously.Luminal contents were collected for 16S rRNA gene sequencing.To minimize confounding effects of inflammation, microbiota analyses were restricted to patients without endoscopic mucosal inflammation.A temperature gradient was observed (cecum > rectum > axilla).Cecal mucosal temperature correlated positively with axillary temperature, whereas rectal temperature did not.Endoscopic inflammation was associated with increased mucosal temperature, particularly in the rectum.Among patients without inflammation, α-and β-diversity did not differ according to mucosal temperature or colonic region.Taxon-specific analyses showed no significant A c c e p t e d M a n u s c r i p t differences after FDR correction.In contrast, Spearman correlation analyses demonstrated significant inverse associations between mucosal temperature and Actinobacteriota-related taxa including Bifidobacteriales (rho = -0.56,q = 0.004), Coriobacteriales (rho = -0.55,q = 0.004), and Corynebacteriales (rho = -0.45,q = 0.017).These findings suggest that colonic mucosal temperature is associated with specific gut microbial taxa, providing new insight into temperature-related modulation of the intestinal microbiome.