A molecular sensor that allows a gut commensal to control its nutrient foundation in a competitive ecosystem

Little is known about how members of the indigenous microflora interact wit h their mammalian hosts to establish mutually beneficial relationships. We have used a gnotobiotic mouse model to show that Bacteroides thetaiotaomicr on, a component of the intestinal microflora of mice and humans, uses a rep ressor, FucR, as a molecular sensor of L-fucose availability. FucR coordina tes expression of an operon encoding enzymes in the L-fucose metabolic path way with expression of another locus that regulates production of fucosylat ed glycans in intestinal enterocytes, Genetic and biochemical studies indic ate that FucR does this by using fucose as an inducer at one locus and as a corepressor at the other locus. Coordinating this commensal's immediate nu tritional requirements with production of a host-derived energy source is c onsistent with its need to enter and persist within a competitive ecosystem .