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Two new xylanases with different substrate specificities from the human gut bacterium Bacteroides intestinalis DSM 17393.

ABSTRACT: Xylan is an abundant plant cell wall polysaccharide and is a dominant component of dietary fiber. Bacteria in the distal human gastrointestinal tract produce xylanase enzymes to initiate the degradation of this complex heteropolymer. These xylanases typically derive from glycoside hydrolase (GH) families 10 and 11; however, analysis of the genome sequence of the xylan-degrading human gut bacterium Bacteroides intestinalis DSM 17393 revealed the presence of two putative GH8 xylanases. In the current study, we demonstrate that the two genes encode enzymes that differ in activity. The xyn8A gene encodes an endoxylanase (Xyn8A), and rex8A encodes a reducing-end xylose-releasing exo-oligoxylanase (Rex8A). Xyn8A hydrolyzed both xylopentaose (X5) and xylohexaose (X6) to a mixture of xylobiose (X2) and xylotriose (X3), while Rex8A hydrolyzed X3 through X6 to a mixture of xylose (X1) and X2. Moreover, rex8A is located downstream of a GH3 gene (xyl3A) that was demonstrated to exhibit ?-xylosidase activity and would be able to further hydrolyze X2 to X1. Mutational analyses of putative active site residues of both Xyn8A and Rex8A confirm their importance in catalysis by these enzymes. Recent genome sequences of gut bacteria reveal an increase in GH8 Rex enzymes, especially among the Bacteroidetes, indicating that these genes contribute to xylan utilization in the human gut.

SUBMITTER: Hong PY

PROVIDER: S-EPMC3993143 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Two new xylanases with different substrate specificities from the human gut bacterium Bacteroides intestinalis DSM 17393.

Hong Pei-Ying PY Iakiviak Michael M Dodd Dylan D Zhang Meiling M Mackie Roderick I RI Cann Isaac I

Applied and environmental microbiology 20140124 7

Xylan is an abundant plant cell wall polysaccharide and is a dominant component of dietary fiber. Bacteria in the distal human gastrointestinal tract produce xylanase enzymes to initiate the degradation of this complex heteropolymer. These xylanases typically derive from glycoside hydrolase (GH) families 10 and 11; however, analysis of the genome sequence of the xylan-degrading human gut bacterium Bacteroides intestinalis DSM 17393 revealed the presence of two putative GH8 xylanases. In the curr ...[more]

PMID: 24463968

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Project description:The utilization of simple sugars is widespread across all domains of life. In contrast, the breakdown of complex carbohydrates is restricted to a subset of organisms. A regulatory paradigm for integration of complex polysaccharide breakdown with simple sugar utilization was established in the mammalian gut symbiont Bacteroides thetaiotaomicron, whereby sensing of monomeric fructose regulates catabolism of both fructose and polymeric fructans. We now report that a different regulatory paradigm governs utilization of monomeric arabinose and the arabinose polymer arabinan. We establish that (i) arabinan utilization genes are controlled by a transcriptional activator that responds to arabinan and by a transcriptional repressor that responds to arabinose, (ii) arabinose utilization genes are regulated directly by the arabinose-responding repressor but indirectly by the arabinan-responding activator, and (iii) activation of both arabinan and arabinose utilization genes requires a pleiotropic transcriptional regulator necessary for survival in the mammalian gut. Genomic analysis predicts that this paradigm is broadly applicable to the breakdown of other polysaccharides in both B. thetaiotaomicron and other gut Bacteroides spp. The uncovered mechanism enables regulation of polysaccharide utilization genes in response to both the polysaccharide and its breakdown products.ImportanceBreakdown of complex polysaccharides derived from "dietary fiber" is achieved by the mammalian gut microbiota. This breakdown creates a critical nutrient source for both the microbiota and its mammalian host. Because the availability of individual polysaccharides fluctuates with variations in the host diet, members of the microbiota strictly control expression of polysaccharide utilization genes. Our findings define a regulatory architecture that controls the breakdown of a polysaccharide by a gut bacterium in response to three distinct signals. This architecture integrates perception of a complex polysaccharide and its monomeric constituent as well as feedback of central metabolism. Moreover, it is broadly applicable to several prominent members of the mammalian gut microbiota. The identified regulatory strategy may contribute to the abundance of gut Bacteroides, despite fluctuations in the host diet.

Dataset Information

Two new xylanases with different substrate specificities from the human gut bacterium Bacteroides intestinalis DSM 17393.

Publications

Two new xylanases with different substrate specificities from the human gut bacterium Bacteroides intestinalis DSM 17393.

Similar Datasets

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