Prioritization of a plant polysaccharide over a mucus carbohydrate is enforced by a Bacteroides hybrid two-component system

Bacteroides is a dominant genus within the intestinal microbiota of healthy humans. Key adaptations of the Bacteroides to the dynamic intestinal ecosystem include a diverse repertoire of genes involved in sensing and processing numerous diet- and host-derived polysaccharides. One such adaptation is the carbohydrate-sensing hybrid two-component system (HTCS) family of signalling sensors, which has been widely expanded within the Bacteroides. Using Bacteroides thetaiotaomicron as a model, we have created a chimeric HTCS consisting of the well-characterized sensing domain of one HTCS, BT1754, and the regulatory domain of another HTCS, BT0366, to explore the regulatory capabilities of these molecules. We found that the BT0366 regulatory region directly binds to and mediates induction of the adjacent polysaccharide utilization locus (PUL) using whole-genome transcriptional profiling after inducing signalling through our chimeric protein. We also found that BT0366 activation simultaneously leads to repression of distal PULs involved in mucus carbohydrate consumption. These results suggest a novel mechanism by which an HTCS enforces a nutrient hierarchy within the Bacteroides via induction and repression of multiple PULs. Thus, hybrid two-component systems provide a mechanism for prioritizing consumption of carbohydrates through simultaneous binding and regulation of multiple polysaccharide utilization loci.