The human gut microbiota provide physiologic attributes that we have not had to evolve on our own, including the ability to process otherwise indigestible dietary polysaccharides. Bacteroides thetaiotaomicron (B. theta), a prominent member of the normal human distal gut microbiota, has an expanded capacity to process both dietary and host-derived polysaccharides, a feature that likely enhances its fitness in the crowded gut ecosystem. A fundamental question is how this prototypic gut symbiont recognizes and adapts to changing carbohydrate availability. The B. theta genome encodes 50 extra-cytoplasmic function sigma (ECF-?) factors, 26 are located adjacent to genes encoding anti-sigma (anti-?) factors, which are predicted transmembrane proteins with periplasmic sensor domains. Most ECF-? /anti-? pairs (25/26) co-localize with a third gene, encoding a SusC-like outer membrane porin. SusC paralogs are implicated in polysaccharide binding and are predicted to interact directly with anti-? factors, comprising a series of cell envelope- spanning switches that transduce external cues (SusC and anti-?) to effect transcriptional changes (ECF-?). My results from in vivo and in vitro experiments indicate that B. theta adapts its physiology to utilize host-derived mucopolysaccharides via an ECF-? /anti-? dependent mechanism. I have identified four prototypic loci (44 genes), each containing an ECF-?/anti-? switch and polysaccharide catabolic functions. I propose to probe the function of these 4 systems by investigating their mechanism(s) and specificity of signal transduction as well as their contribution B. theta fitness in the mouse intestine.
Aim 1 will test a working model of ECF-?/anti-? signal transduction through genetic disruption of its predicted components and subsequent assay of function. Yeast 2-hybrid analysis will be used to probe predicted protein-protein interactions between signaling components and, because these signaling components are expanded in B. theta, the potential for cross-talk between paralogs.
Aim 2 seeks to chemically define mucopolysaccharide components that trigger ECF-?/anti-? switches and, in conjunction with a bioassay for locus induction, will provide valuable insight into the chemical language through which B. theta perceives its environment.
Aim 3 addresses the hypothesis that mucopolysaccharide utilization by B. theta enhances in vivo fitness. The ability of B. theta to turn on these systems will be eliminated through genetic manipulations, and the colonization behavior of mutants evaluated in competition with wild-type B. theta in gnotobiotic mice. These studies will expand our understanding of how bacteria inhabiting the gut can shift their metabolism to coincide with changing availability of carbohydrate resources in the intestine. ? ? ?
| Martens, Eric C; Lowe, Elisabeth C; Chiang, Herbert et al. (2011) Recognition and degradation of plant cell wall polysaccharides by two human gut symbionts. PLoS Biol 9:e1001221 |
| Martens, Eric C; Roth, Robyn; Heuser, John E et al. (2009) Coordinate regulation of glycan degradation and polysaccharide capsule biosynthesis by a prominent human gut symbiont. J Biol Chem 284:18445-57 |
| Martens, Eric C; Koropatkin, Nicole M; Smith, Thomas J et al. (2009) Complex glycan catabolism by the human gut microbiota: the Bacteroidetes Sus-like paradigm. J Biol Chem 284:24673-7 |
| Martens, Eric C; Chiang, Herbert C; Gordon, Jeffrey I (2008) Mucosal glycan foraging enhances fitness and transmission of a saccharolytic human gut bacterial symbiont. Cell Host Microbe 4:447-57 |
