MILIEU INTÉRIEUR. “Ample evidence shows that microbes act directly as agents of postembryonic development. For example, fucosyltransferases decorate the surface of the embryonic mammalian intestine with fucose residues that provide a nutrient source for gut microbes, including B. thetaiotaomicron, as they colonize the newborn.”
http://www.pnas.org/content/110/9/3229.full