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Trends Microbiol. 2004 Jan;12(1):21-8.

Message from a human gut symbiont: sensitivity is a prerequisite for sharing.

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Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110, USA.


Microbial genome sequencing projects are beginning to provide insights about the molecular foundations of human-bacterial symbioses. The intestine contains our largest collection of symbionts, where members of Bacteroides comprise approximately 25% of the microbiota in adults. The recently defined proteome of a prominent human intestinal symbiont, Bacteroides thetaiotaomicron, contains an elaborate environmental-sensing apparatus. This apparatus includes an unprecedented number of extracytoplasmic function (ECF) sigma-factors, and a large collection of novel hybrid two-component systems composed of membrane-spanning periplasmic proteins with histidine kinase, phosphoacceptor, response regulator receiver and DNA-binding domains. These sensors are linked to the organism's large repertoire of genes involved in acquiring and processing dietary polysaccharides ('the glycobiome'). This arrangement illustrates how a successful symbiont has evolved strategies for detecting and responding to conditions in its niche so that it can sustain beneficial relationships with its microbial and human partners.

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