Modeling and pathway analysis of [U‐13C]starch conversion by a colonic microbiota

Abstract

We study colonic microbial diversity, metabolic function of colonic microbes, the way diet affects metabolic fluxes, and how produced metabolites affect human health. Short chain fatty acids (SCFA) and especially butyrate, produced by the colonic microbiota, are important mediators of health and disease. Linking the biosynthesis of SCFA to specific gut microbial pathways holds promise for the development of prebiotics that specifically modulate these pathways in vivo. Therefore, 13C stable isotope labeling, NMR, and mathematical modeling of isotopomer distributions were employed to investigate colonic microbial metabolic pathway activities during [U‐13C]starch conversion in an in vitro model of the colon inoculated with a standardised fresh human fecal microbiota. GC‐MS, enzymatic methods and NMR at 500 MHz were used to identify microbial metabolites and to analyze their 13C contents.The SCFA acetate, propionate and butyrate were determined as the principal starch degradation products. Quantitative insight in bacterial metabolic routes was obtained from analysis of 13C‐13C coupling patterns in 2D HSQC spectra that resulted from incorporation of intact 13C glucose backbone fragments in SCFA. These indicated that e.g. propionate was almost exclusively formed via the succinate pathway.In conclusion, this stable isotope study underlines the importance of colonic bacterial SCFA metabolism.