Background:Irritable bowel syndrome (IBS) is the most prevalent functional gastrointestinal (GI)disorder,affecting ~10% of the world populations.Also the comorbidity of IBS with psychological distress is common.The pathophysiological mechanisms have been investigated on animal models,which found close correlations with dys-regulation of brain-gut axis,impaired mucosal barrier function and alteration in gastrointestinal microbiota.Previous research have identified altered fecal microbiota in either IBS or depression,but the relationships of gut microbiota between diarrhea-predominant IBS (IBS-D) and depression patients have been poorly defined.The present study aimed to identify the microbiota profiles in IBS,depression,comorbidity of IBS and depression (COMO) patients,and healthy controls,clarify the microbial relationship between IBS and depression,explore the correlation between microbial variation and clinical and pathophysiological features.Thus provide new insights into the pathogenicity of IBS and depression.