Diet and Metabolism of the Intestinal Flora

Abstract

Diet is an important factor that determines the composition of bacterial populations in the colonic microbiota, as well as affecting their abilities to carry out many biochemical transformations. Starches that escape digestion in upper gut and non-starch polysaccharides (dietary fibre) are quantitatively the most important substrates for intestinal bacteria. Carbohydrate fermentation is one of thekey events in the large bowel, especially SCFA production. Because the majority of intestinal microorganisms are saccharolytic, carbohydrate metabolism interacts with other biochemical processes mediated by the microflora, such as protein breakdown and amino acid formation, where it has a protective effect against the often toxic products of putrefaction. In many species, the breakdown of complex polysaccharides and the synthesis and activities of substrate uptake systems is controlled by catabolite regulatory mechanisms. The factors that govern fermentation product fermentation are multifactorial, including the anatomy of the colonitself, the types and amounts of food consumed by the host, ecological interactions between different groups of bacteria, individual bacterial strategies for acquiring substrate and their catabolic processes. Substrate availability and bacterial growth rates have been shown to strongly affect fermentation product formation in chemostat studies with Clostridium perfringens, Bacteroides ovatus and Bifidobacterium breve, where high growth rates and high levels of substrate predispose towards the production of electron sink products such as lactate and succinate. Bacterial populations growing in biofilmson the surfaces of digestive residues in the gut lumen were found to be phylogenetically similar to non-adherentcommunities, but were biochemically distinct with respect to enzyme synthesis and fermentation product formation.