Roles of the Commensal Microbiota

A major role of the microbiota is to ferment nondigestible dietary components and endogenous mucus produced by the gut epithelium. This is an example of a symbiotic relationship as the human host benefits from a wide array of microbial enzymes which are outside the host s own biochemical repertoire. This provides the host with a source of 

The main fermentation end products are short chain fatty acids (SCFA) which are small organic molecules absorbed by diffusion carriers mediated exchange or ion exchange processes. Common examples include acetate, butyrate, and propionate, and are considered mairrly as compotmds which provide a source of energy to the host. Fermentation activity differs according to area within the gut, the most metaboli- 

Proxlmal colon High concentration of substrates Saccharolysis Acid pH (5-6) 

Rapid bacterial growth FIGURE 2.1. Fermentation in the coton. Fermentation activity differs according to the specific iocation within the gut. The most metaboiicatiy active area is the caecum and right (proximai) coton. The ieft side has a different pH which favors a more proteoiytic fermentation (Gibson and Roberfroid 1995). 

---