Comprehensive relationships between gut microbiome and faecal metabolome in individuals with type 2 diabetes and its complications

As the treatment regimens such as metformin could confound the correlation between type 2 diabetes (T2D) and gut microbiome, we should revisit the relationship between gut microbiota and T2D patients who are not currently treated with metformin. The study recruited 65 T2D patients: 49 with and 16 without diabetic complications, and 35 healthy controls. We sequenced the 16S rRNA V3-V4 region of gut microbiota and detected metabolites based on liquid chromatography mass spectrometry (LC/MS) and gas chromatography mass spectrometry (GC/MS) in faecal samples. The composition of both the gut microbiota and faecal metabolites changed significantly with T2D patients. The abundance of Proteobacteria and the ratio of Firmicutes/Bacteroidetes were higher in T2D patients than healthy subjects, and the short chain fatty acids (SCFAs), bile acids and lipids of T2D patients were significantly disordered. Moreover, the abundances of certain SCFA-producing bacteria (Lachnospiraceae and Ruminococcaceae etc.) were significantly increased in T2D patients, while the faecal SCFAs concentrations were significantly decreased. It’s suggested that the role of SCFA-producing bacteria was not simply to produce SCFAs. Then we identified 44 microbial modules to explore the correlations between the gut microbiota and metabolic traits. Specially, most modules including certain SCFA-producing bacteria were comprehensively correlated to body mass index, the levels of blood glucose, blood pressure, blood cholesterol and faecal bile acids and lipids. Our study identified the relationships between the gut microbiota and faecal metabolites, and provided a resource for future studies to understand host–gut microbiota interactions in T2D.