Editors' ChoiceMicrobiology

Gut Bug's Sensors Bag Us Carbs

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Science's STKE  13 Jun 2006:
Vol. 2006, Issue 339, pp. tw198
DOI: 10.1126/stke.3392006tw198

Bacteria make heavy use of two-component regulatory systems to sense external signals. The membrane-localized sensor proteins have histidine kinase and phosphoacceptor domains and communicate to intracellular response regulators, which often act as transcription factors. There are also hybrid two-component systems (HTCSs), which are really "one-component," because the sensor and response regulator sequences are combined. Sonnenburg et al. analyzed the function of an HTCS in Bacteroides thetaiotaomicron, a bacterium that inhabits the human gut. Such bacteria are required for digestion of dietary polysaccharides. The human genome has a meager supply of the required hydrolases and lyases for such digestion, whereas B. thetaiotaomicron's genome encodes more than 200 of the former and more than a dozen of the latter. The gene encoding the HTCS BT3172 was detected in a screen for genes whose expression was enhanced in bacteria residing in the gut of rats eating a diet high in polysaccharides. Loss of BT3172 caused decreased expression of α-mannosidase genes, and expression of BT3172 was enhanced by exposure of bacteria to mannosides. The predicted structure of BT3172 has three transmembrane domains and would result in sensor regions on the periplasmic and cytoplasmic sides of the bacterial inner membrane. The periplasmic sensor might sense mannosides in the environment. The authors used a yeast two-hybrid screen to detect binding partners for the cytoplasmic sensor domain of BT3172 and detected two proteins involved in glucose metabolism--glucose 6-phosphate isomerase and glucose 6-phosphate dehydrogenase. Thus, the authors speculate that BT3172 may serve to coordinate carbohydrate use and availability. They propose that more complete understanding of gut bacteria could allow "personalized nutrition where diet is matched to the nutrient processing capacity of an individual's microbiota."

E. D. Sonnenburg, J. L. Sonnenburg, J. K. Manchester, E. E. Hansen, H. C. Chiang, J. I. Gordon, A hybrid two-component system protein of a prominent human gut symbiont couples glycan sensing in vivo to carbohydrate metabolism. Proc. Natl. Acad. Sci. U.S.A. 103, 8834-8839 (2006). [Abstract] [Full Text]

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