BIOME REGULATION OF TASTE RECEPTORS. Sweet taste receptor genes in taste buds in the mouth can be down-regulated by bacterially-derived lipopolysaccharides, which modulates the transmission of taste input to the brain. This is a direct connection, at least in mice, between oral taste receptors and the microbiome.
http://www.researchgate.net/publication/258443568_Ingestion_of_bacterial_lipopolysaccharide_inhibits_peripheral_taste_responses_to_sucrose_in_mice