Complex carbohydrate utilization by gut bacteria modulates host food preference

The gut microbiota interacts directly with dietary nutrients and has the ability to modify host feeding behavior, but the underlying mechanisms remain poorly understood. Select gut bacteria digest complex carbohydrates that are non-digestible by the host and liberate metabolites that serve as additional energy sources and pleiotropic signaling molecules. Here we use a gnotobiotic mouse model to examine how differential fructose polysaccharide metabolism by commensal gut bacteria influences host preference for diets containing these carbohydrates. Bacteroides thetaiotaomicron and Bacteroides ovatus selectively ferment fructans with different glycosidic linkages: B. thetaiotaomicron ferments levan with {beta}2-6 linkages, whereas B. ovatus ferments inulin with {beta}2-1 linkages. Since inulin and levan are both fructose polymers, inulin and levan diet have similar perceptual salience to mice. We find that mice colonized with B. thetaiotaomicron prefer the non-fermentable inulin diet, while mice colonized with B. ovatus prefer the non-fermentable levan diet. Knockout of bacterial fructan utilization genes abrogates this preference, whereas swapping the fermentation ability of B. thetaiotaomicron to inulin confers host preference for the levan diet. Bacterial fructan fermentation and host behavioral preference for the non-fermentable fructan are associated with increased neuronal activation in the arcuate nucleus of the hypothalamus, a key brain region for appetite regulation. These results reveal that selective nutrient metabolism by gut bacteria contributes to host associative learning of dietary preference, and further informs fundamental understanding of the biological determinants of food choice.