Fig. 3: Metabolic responses of human gut microbiota to two-week intake of potato starch (pSt).

a A representative image of colonizing B. adolescentis on fecal starch granules, which are visible as round dark areas (approx. diameter 20–50 μm). Green: Bifidobacterium, red: B. adolescentis, blue: total bacteria. Bar = 50 μm. b Excreted starch granules in fecal sections. Representative images of iodine-stained fecal sections during the pSt intake period from a B. adolescentis carrier and non-carrier. Difference in % area of excreted starch granules between the pre-intake and intake periods is shown in a graph. Horizontal bars indicate medians. * Two-tailed Welch’s t test. Arrowheads: starch granules (omitted in non-carrier). Bars = 1 mm. c SCFA concentrations before and during pSt intake in B. adolescentis carriers and non-carriers. Elements of box plots are as follows: horizontal bar, median; box limits, upper and lower quartiles; whiskers, 1.5× interquartile range. P values are based on Wilcoxon test and are adjusted using the Benjamini–Hochberg procedure. d Taxa that correlate highly with each SCFA as determined by Spearman’s correlation analysis. Given that the aim of this analysis was to reveal major producers of each SCFA, only OTUs with >0.5% average relative abundance and p < 0.05 are labeled. Three known starch-utilizing species are shown as colored dots. e Taxa that correlated (p < 0.05) with B. adolescentis, E. rectale, or R. bromii as determined by Spearman’s correlation analysis. Only OTUs with >0.5% average relative abundance and detected in more than half of the samples are shown. Orange: positive correlation, blue: negative correlation. Node size is proportional to the relative abundance of the OTU, and edge width is proportional to the correlation coefficient (Spearman’s ρ).