In addition, propionate and butyrate, as metabolites of R. hominins, promote intestinal melatonin synthesis by promoting 5-hydroxytryptamine (HT) synthesis and activating the phosphorylated-cAMP response element-binding protein (p-CREB)-arylalkylamine N-acetyltransferase (AANAT) pathway, thus, offering a potential target for ameliorating intestinal diseases (Song et al., 2021). Here, AANAT is linked to intestinal disorder.