MUC5AC and colorectal carcinoma: Butyrate is mainly produced by Firmicutes bacteria and is the preferred metabolic substrate for colon epithelial cells, whereas acetate and propionate are predominantly produced by Bacteroidetes.72 The role of butyrate in regulating mucin expression was evaluated in the HT29-Cl.16E CRC cell line (derived from HT-29) cultured in glucose-enriched media.