Unknown,Transcriptomics,Genomics,Proteomics

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Depolymerization of plant cell wall glycans by symbiotic human gut bacteria (Bacteroides ovatus)

ABSTRACT: Symbiotic bacteria inhabiting the distal human gut have evolved under intense pressure to utilize complex carbohydrates, predominantly plant cell wall glycans abundant in our diets. These substrates are recalcitrant to depolymerization by digestive enzymes encoded in the human genome, but are efficiently targeted by some of the ~103-104 bacterial species that inhabit this niche. These species augment our comparatively narrow carbohydrate digestive capacity by unlocking otherwise unusable sugars and fermenting them into host-absorbable forms, such as short-chain fatty acids. We used phenotype profiling, whole-genome transcriptional analysis and molecular genetic approaches to investigate complex glycan utilization by two fully sequenced and closely related human gut symbionts: Bacteroides thetaiotaomicron and Bacteroides ovatus. Together these species target all of the common glycosidic linkages found in the plant cell wall, as well as host polysaccharides, but each species exhibits a unique ‘glycan niche’: in vitro B. thetaiotaomicron targets plant cell wall pectins in addition to linkages contained in host N- and O-glycans; B. ovatus uniquely targets hemicellulosic polysaccharides along with several pectins, but is deficient in host glycan utilization. Bacteroides ovatus bacteria were grown either in vitro on defined complex glycan sources, or in vivo in the intestinal tract of gnotobiotic mice fed variable diets. Increased in vitro gene expression was used to indicate the genes required for metabolism of complex glycans and compared to in vivo transcriptional activity to determine expression in the mouse gut.

ORGANISM(S): Bacteroides ovatus

SUBMITTER: Eric Martens

PROVIDER: E-GEOD-25575 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:The adult human gut microbial community is typically dominated by two bacterial phyla (divisions), the Firmicutes and the Bacteroidetes. Little is known about the factors that govern the interactions between their members. Here we examine the niches of representatives of both phyla in vivo. Finished genome sequences were generated from E. rectale and E. eligens, which belong to Clostridium Cluster XIVa, one of the most common gut Firmicute clades. Comparison of these and 25 other gut Firmicutes and Bacteroidetes indicated that the former possess smaller genomes and a disproportionately smaller number of glycan-degrading enzymes. Germ-free mice were then colonized with E. rectale and/or a prominent human gut Bacteroidetes, Bacteroides thetaiotaomicron, followed by whole genome transcriptional profiling of both organisms in their distal gut (cecal) habitat as well as host responses, high resolution proteomic analysis of cecal contents, and biochemical assays of carbohydrate metabolism. B. thetaiotaomicron adapts to E. rectale by upregulating expression of a variety of polysaccharide utilization loci (PULs) encoding numerous glycoside hydrolase gene families, and by signaling the host to produce mucosal glycans that it, but not E. rectale, can access. E. rectale adapts to B. thetaiotaomicron by decreasing production of its glycan-degrading enzymes, increasing expression of selected amino acid and sugar transporters, and facilitating glycolysis by reducing levels of NADH, in part via generation of butyrate from acetate, which in turn is utilized by the gut epithelium. This simplified model of the human gut microbiota illustrates niche specialization and functional redundancy within members of major gut bacterial phyla, and the importance of host glycans as a nutrient foundation that ensures ecosystem stability. The interactions between E. rectale and B. thetaiotaomicron were characterized by performing whole genome transcriptional profiling of each species after colonization of gnotobiotic mice with each organism alone, or in combination. E. rectale was also profiled during in vitro growth.

Project description:The adult human gut microbial community is typically dominated by two bacterial phyla (divisions), the Firmicutes and the Bacteroidetes. Little is known about the factors that govern the interactions between their members. Here we examine the niches of representatives of both phyla in vivo. Finished genome sequences were generated from E. rectale and E. eligens, which belong to Clostridium Cluster XIVa, one of the most common gut Firmicute clades. Comparison of these and 25 other gut Firmicutes and Bacteroidetes indicated that the former possess smaller genomes and a disproportionately smaller number of glycan-degrading enzymes. Germ-free mice were then colonized with E. rectale and/or a prominent human gut Bacteroidetes, Bacteroides thetaiotaomicron, followed by whole genome transcriptional profiling of both organisms in their distal gut (cecal) habitat as well as host responses, high resolution proteomic analysis of cecal contents, and biochemical assays of carbohydrate metabolism. B. thetaiotaomicron adapts to E. rectale by upregulating expression of a variety of polysaccharide utilization loci (PULs) encoding numerous glycoside hydrolase gene families, and by signaling the host to produce mucosal glycans that it, but not E. rectale, can access. E. rectale adapts to B. thetaiotaomicron by decreasing production of its glycan-degrading enzymes, increasing expression of selected amino acid and sugar transporters, and facilitating glycolysis by reducing levels of NADH, in part via generation of butyrate from acetate, which in turn is utilized by the gut epithelium. This simplified model of the human gut microbiota illustrates niche specialization and functional redundancy within members of major gut bacterial phyla, and the importance of host glycans as a nutrient foundation that ensures ecosystem stability. We assessed how E. rectale and B. thetaiotaomicron were affected by changes in host diet. Groups of age- and gender-matched co-colonized mice were fed one of three diets that varied primarily in their carbohydrate and fat content: (i) the standard low-fat, plant polysaccharide-rich diet used for the experiments described above (abbreviated âLF/PPâ for low-fat/plant polysaccharide), (ii) a high-fat, âhigh-sugarâ Western-type diet (abbreviated HF/HS) that contained sucrose, maltodextrin, corn starch as well as complex polysaccharides (primarily cellulose) that were not digestible by B. thetaiotaomicron or E. rectale, and (iii) a control diet that was similar to (ii) except that the fat content was 4-fold lower (âLF/HSâ for low-fat, high-sugar; n=5 mice per group).

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Depolymerization of plant cell wall glycans by symbiotic human gut bacteria (Bacteroides ovatus)

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