Fermentations by saccharolytic intestinal bacteria

Abstract

Most nonsporing anaerobes of the intestinal tract use the Embden-Meyerhof-Parnas scheme to ferment carbohydrates. Almost all of them oxidize pyruvate, the key fermentation intermediate, to acetyl coenzyme A and CO₂ with reduction of a low-potential electron acceptor. H₂ is formed from the low potential acceptor or from NADH. Pyruvate is a precursor of lactate, and phosphoenolpyruvate is a precursor of succinate and propionate. Ethanol, acetate, and butyrate are formed from acetyl coenzyme A. Formate is produced by reduction of CO₂ by Ruminococcus albus. Heme is required by human Bacteroides for the formation of succinate and, in the presence of vitamin B₁₂, propionate. A fermentation equation derived from the concentration of volatile acids found in human feces suggests that the fermentation in the large intestine is similar to the rumen fermentation.