Fig. 4.

Changing nutrient intake affects microbiota composition and SCFA availability. The spatiotemporal dynamics of bacterial growth was analyzed for different rates of nutrient influx (N_in, in millimoles of glucose equivalents per day). (A) Relative abundance of Bacteroidetes and Firmicutes in the distal colon (mimicking “fecal” content), depending on nutrient influx. (B) pH profiles along the length of the colon; each colored line represents the result of a specific nutrient influx. (C) Epithelial uptake of different SCFAs (integrated along the length of the colon) for different nutrient influx. SCFA ratios are calculated based on measured excretion rates (Fig. 1A) and model results for phyla composition in A. Table provides the relationship between the nutrient influx (N_in), their corresponding energy content (E_in), and the amount of energy taken up by the epithelium in the form of SCFAs (E_up). The case of N_in = 300 mmol/d corresponds to the results shown in Fig. 3. Other parameters are as in SI Appendix, Tables S1 and S2. Values in A for position x = 1.89 m (end of colon). Values in C estimated by average excretion profiles of different strains (Fig. 1A and SI Appendix, section 5.7). Simulation for 120 h. Profiles of other variables are shown in SI Appendix, Fig. S7 A–C.