||P.8 left column: "Bile acids are classical examples of trans-genomic metabolites arising from the interactive metabolism between the host genome and the gut microbiome. As outlined in Fig. 3, bile acids are synthesised in the liver from cholesterol to form the two primary bile acids cholic acid (CA) and chenodeoxycholic acid (CDCA). Prior to secretion into bile, N-acyl amidation occurs conjugating the carboxyl group of the bile acids to a molecule of either taurine or glycine. This conjugation step produces a molecule that is fully ionised at physiologic pH, enhancing the amphipathic nature and, therefore, detergent properties of the molecule. Upon ingestion of a meal, bile acids stored in the gall bladder are secreted into the small intestine to facilitate lipid digestion and absorption. While the majority of bile acids are actively absorbed in the distal ileum and recycled back to the liver, a small fraction (1–5%, 200–800 mg daily in humans) escapes this enterohepatic circulation and enters the colon." P.9 left column 2nd paragraph: "Microbial biotransformation of bile acids includes
modification to both the side chain and the steroid nucleus (Fig. 3)."