Figure 2.

Mass Flows in the Host-Associated Microbiota. (A) Schematic of general mass flows in the gut ecosystem, from diet to and between host and microbiota. (B) Conceptual example of how stable-isotope probing (SIP) can be used to specifically track isotopically labeled microbes involved in ¹³C-starch degradation or downstream in the trophic cascade, and to follow the fate of starch degradation metabolism and products in the microbiota and host (red indicates ¹³C in compounds and biomass). Intestinal metabolites are absorbed and metabolized by the epithelium and/or further distributed to peripheral host tissues and organs (e.g., liver, kidney, brain) by the circulation. SCFA, short-chain fatty acid.