Amino Acid-Derived Bacterial Metabolites in the Colorectal Luminal Fluid: Effects on Microbial Communication, Metabolism, Physiology, and Growth

Undigested dietary and endogenous proteins, as well as unabsorbed amino acids, can move from the terminal part of the ileum into the large intestine, where they meet a dense microbial population. Exfoliated cells and mucus released from the large intestine epithelium also supply nitrogenous material to this microbial population. The bacteria in the large intestine luminal fluid release amino acids from the available proteins, and amino acids are then used for bacterial protein synthesis, energy production, and in other various catabolic pathways. The resulting metabolic intermediaries and end products can then accumulate in the colorectal fluid, and their concentrations appear to depend on different parameters, including microbiota composition and metabolic activity, substrate availability, and the capacity of absorptive colonocytes to absorb these metabolites. The aim of the present review is to present how amino acid-derived bacterial metabolites can affect microbial communication between both commensal and pathogenic microorganisms, as well as their metabolism, physiology, and growth.