Supplementary Table 1. Demografic data for the IBS (A) and control (B) populations under study. F, female; M, male. Supplementary figure 1. Principal coordinates analysis of weighted (A) and unweighted (B) Unifrac distances based on 16S rRNA gene profiling data. Lines connect samples belonging to the same patient. The first two coordinates (PC1 and PC2) are displayed with the percentage of variance explained in brackets. Supplementary figure 2. Principal coordinates analysis of Unifrac distances based on 16S rRNA gene profiling data of a single fecal sample collected from 40 IBS patients. The first two coordinates (PC1 and PC2) are displayed with the percentage of variance explained in brackets. Supplementary figure 3. Within‐subject (alpha) diversity of fecal samples from IBS patients determined through four different estimators. Scatter dot plots show data from a single fecal sample per subject (panel A; n = 40) and medians of the data from five fecal samples per subject (panel B, n = 39). Statistical significances are according to Mann‐Whitney test. Supplementary figure 4. Analyses of enterotypes in IBS fecal samples. A, Principal Coordinates Analysis (PCoA; the first two principal components are shown). The optimal number of clusters was determined through the Calinski‐Harabasz (CH) index and the Silhouette coefficient. Supplementary figure 5. Tukey boxplots of the dominant bacterial genera and orders in IBS fecal samples (n=40; panel A) and healthy control subjects (n=16; B). Supplementary figure 6. OTUs distinguishing IBS subtypes determined by using the DESeq2 negative binomial distribution method on 16S rRNA gene profiling data of a single fecal sample per patient. The colors in the heatmap represents the mean of normalized relative abundances of the reported OTUs. The taxonomic lineage of each taxon is shown; p, phylum; c, class; o, order; f, family; g, genus; s, species. Positive fold changes (shown on a red background) indicate OTU overrepresentation in IBS‐U (panels A and B) and IBS‐C (panel C); negative fold changes (shown on a blue background) indicate an increase of OTU relative abundance in IBS‐C (panel A) and IBS‐D (panel B and C). Supplementary figure 7. Levels of short chain fatty acids determined in a single fecal sample per IBS patient (n=40) and healthy control (n=25; data from Gargari et al., 2016). Statistical significances are according to Mann‐Whitney test; *, P<0.05; **, P<0.01.