Gut Bacteria Mediate Nutrient Availability in Drosophila Diets

Abstract

Drosophila melanogaster gut microbes play important roles in host nutritional physiology. However, these associations are often indirect and studies typically are in the context of specialized nutritional conditions, making it difficult to discern how microbiome-mediated impacts translate to physiologically relevant conditions, in the laboratory or nature. In this study, we quantified changes in dietary nutrients due to D. melanogaster gut bacteria on three artificial diets and a natural diet of grapes. We show that in all four diet conditions, bacteria altered protein, carbohydrates, and moisture of the food substrate. In depth analysis on one diet revealed that bacteria also increased tryptophan levels, an essential amino acid encountered scarcely in nature. These nutrient changes result in an increased protein to carbohydrate (P:C) ratio in all diets, which we hypothesized to be a significant determinant of microbiome-mediated host nutritional physiology. To test this, we compared life history traits of axenic flies reared on the three artificial diets with increased P:C or continuous bacterial inoculation. We found that, while on some diets an environment of nutritional plenitude had impacts on life history, it did not fully explain all microbiome-associated phenotypes. This suggests that other factors, such as micronutrients and feeding behavior, likely also contribute to life history traits in a diet-dependent manner. Thus, while some bacterial impacts on nutrition occur across diets, others are dictated by unique dietary environments, highlighting the importance of diet-microbiome interactions in D. melanogaster nutritional physiology. Importance Both in the laboratory and in nature, D. melanogaster-associated microbes serve as nutritional effectors, either through production of metabolites or as direct sources of protein biomass. The relationship between the microbiome and resulting host nutritional physiology is significantly impacted by diet composition, yet studies involving D. melanogaster are performed using a wide range of artificial diets, making it difficult to discern which aspects of host-microbe interactions may be universal or diet-dependent. In this study, we utilized three standard D. melanogaster diets and a natural grape diet to form a comprehensive understanding of the quantifiable nutritional changes mediated by the host microbial community. We then altered these artificial diets based on the observed microbe-mediated changes to demonstrate their potential to influence host physiology, allowing us to identify nutritional factors whose effects were either universal for the three artificial diets or dependent on host diet composition.

The gut microbiome influences host diet selection behavior

“…Specifically, our study provides evidence that variation in the gut microbiota alters host nutrient availability and can yield significant differences in the diet selection of conventionalized mice in just 11 days, likely through differential bacterial metabolism and downstream availability of EAAs, especially tryptophan. These findings are largely consistent with recent mechanistic work in model systems 9,38 , but address the natural variation in microbial communities that exist among individuals and across species 11,12 .…”

Drosophila Antimicrobial Peptides and Lysozymes Regulate Gut Microbiota Composition and Abundance

“…Innate immunity is a key regulator of microbial abundance in Drosophila ( 22 – 25 ). Upon acute bacterial infection, Drosophila immune responsive tissues (the fat body and hemocytes in systemic infection, and epithelium in local infection) sense microbe-associated molecular patterns (MAMPs) to activate signaling pathways.…”

Drosophilaantimicrobial peptides and lysozymes regulate gut microbiota composition and abundance

“…Innate immunity is a key regulator of microbial abundance in Drosophila (22)(23)(24)(25). Upon acute bacterial infection, Drosophila immune responsive tissues (the fat body and hemocytes in systemic infection, and epithelium in local infection) sense microbe-associated molecular patterns (MAMPs) to activate signaling pathways.…”