Life span and reproductive success can depend on controlling dietary protein intake. Yet the importance of gut microbial symbionts in appetite control is not understood. Leitão-Gonçalves et al. used the fruitfly, Drosophila, to test what influence their microbiota might have on food choice. Fruitflies like sugar, but after they have mated, they prefer to eat yeast to gain essential amino acids for egg-making. By knocking out the phenylalanine hydroxylase gene, flies can be duped into sensing that tyrosine is an essential amino acid. If tyrosine is missing from a chemically defined diet, the engineered flies' fecundity falls and, if given the choice, they will voraciously eat yeast to compensate for the missing nutrient. If particular live microbiota species (Acetobacter pomorum and lactobacilli) are introduced into the food of the engineered flies, they lose their taste for yeast and resume egg-laying. Unexpectedly, the microbiota do not seem to directly provide a compensatory source of the missing amino acid. The precise mechanism for the protective effect of the microbiota remains elusive.
PLOS Biol. 10.1371/journal.pbio.2000862 (2017).