Glutamine enhances sucrose taste through a gut microbiota-gut-brain axis in Drosophila

Amino acids (AAs) are known to play important roles in various physiological functions. However, their effect on sweet taste perception remains largely unknown.We used Drosophila to evaluate the effect of each AA on sucrose taste perception. Individual AA was supplemented into diets and male flies were fed on these diets for 6 days. The proboscis extension response (PER) assay was applied to assess the sucrose taste sensitivity of treated flies. We further utilized the RNA-seq and germ-free (GF) flies to reveal the underlying mechanisms of sucrose taste sensitization induced by glutamine (Gln).We found that supplementation of Gln into diets significantly enhances sucrose taste sensitivity. This sucrose taste sensitization is dependent on gut microbiota and requires a specific gut bacterium Acetobacter tropicalis (A. tropicalis). We further found that CNMamide (CNMa) in the gut and CNMa receptor (CNMaR) in dopaminergic neurons are required for increased sucrose taste sensitivity by Gln diet. Finally, we demonstrated that a gut microbiota-gut-brain axis is required for Gln-induced sucrose taste sensitization.These findings can advance understanding of the complex interplay between host physiology, dietary factors, and gut microbiota.