During the last years, alterations in the composition of gut microbiota (the population of microorganisms that colonizes the human intestinal tract) have been associated with different human pathologies ranging from luminal, metabolic and allergic diseases to neurodevelopmental illnesses. Recently, the gut microbiota was unexpectedly shown to induce the expression of the flavoenzyme D-amino acid oxidase and its secretion by intestinal epithelial cells. DAAO in turn was proposed to control the microbiota homeostasis through the hydrogen peroxide generated by the oxidative deamination of D-amino acids, derived from diet or the microbial cell wall.

However, we propose an alternative mechanism in the DAAO-mediated selection of gut microbiota: we identified two putative antimicrobial peptides in the flavoenzyme’s primary structure. These peptides show antimicrobial activity on Gram-positive and Gram-negative  bacteria.  These peptides are also present in the gut.

Further studies performed in collaboration with a number of reserch groups, indicate that the proteolytic digestion of the secreted DAAO yields to the release of the antibacterial peptides which then affect the microbiota composition.