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Glycan complexity dictates microbial resource allocation in the large intestine.

Rogowski A, Briggs JA, Mortimer JC, Tryfona T, Terrapon N, Lowe EC, Baslé A, Morland C, Day AM, Zheng H, Rogers TE, Thompson P, Hawkins AR, Yadav MP, Henrissat B, Martens EC, Dupree P, Gilbert HJ, Bolam DN - Nat Commun (2015)

Bottom Line: We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan.Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains.Our report presents a highly complex and dynamic xylan degrading apparatus that is fine-tuned to recognize the different forms of the polysaccharide presented to the human gut microbiota.

View Article: PubMed Central - PubMed

Affiliation: Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.

ABSTRACT
The structure of the human gut microbiota is controlled primarily through the degradation of complex dietary carbohydrates, but the extent to which carbohydrate breakdown products are shared between members of the microbiota is unclear. We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan. Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains. Our report presents a highly complex and dynamic xylan degrading apparatus that is fine-tuned to recognize the different forms of the polysaccharide presented to the human gut microbiota.

No MeSH data available.


Related in: MedlinePlus

The ability of other members of the microbiota to use PBPs released by B. ovatus during growth on xylan is determined by the complexity of the polysaccharide.Bacteroides ovatus (Bo) and Bifidobacterium adolescentis were co-cultured on BGX (a) WAX (b) and CX (c) and the number of CFUs of each determined at different points on the growth curve. (d) Shows the CFU ml-1 of B. ovatus alone at different phases of growth. Note, when the Bifidobacterium alone was grown on digested xylans (see Supplementary Fig. 8), the CFU ml−1 at late exponential phase (OD600 ∼1.2) was ∼8.0 × 108, indicating that ∼25% of the total xylan is used by B. adolescentis. (e) Growth of B. ovatus wild type and the ΔGH98 mutant (BACOVA_03433) on CX (0.5% w/v). Pre-digested indicates the CX was digested to completion with the GH98 xylanase prior to addition to the media. (f) Tagged strains of wild-type B. ovatus and the ΔGH98 mutant were co-cultured on CX (see panel e for growth curve). Samples were taken at different time points and qPCR with primers unique to each strain was used to determine the ratio of each in the culture. Each data point is the average and s.d. of triplicate growths.
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f9: The ability of other members of the microbiota to use PBPs released by B. ovatus during growth on xylan is determined by the complexity of the polysaccharide.Bacteroides ovatus (Bo) and Bifidobacterium adolescentis were co-cultured on BGX (a) WAX (b) and CX (c) and the number of CFUs of each determined at different points on the growth curve. (d) Shows the CFU ml-1 of B. ovatus alone at different phases of growth. Note, when the Bifidobacterium alone was grown on digested xylans (see Supplementary Fig. 8), the CFU ml−1 at late exponential phase (OD600 ∼1.2) was ∼8.0 × 108, indicating that ∼25% of the total xylan is used by B. adolescentis. (e) Growth of B. ovatus wild type and the ΔGH98 mutant (BACOVA_03433) on CX (0.5% w/v). Pre-digested indicates the CX was digested to completion with the GH98 xylanase prior to addition to the media. (f) Tagged strains of wild-type B. ovatus and the ΔGH98 mutant were co-cultured on CX (see panel e for growth curve). Samples were taken at different time points and qPCR with primers unique to each strain was used to determine the ratio of each in the culture. Each data point is the average and s.d. of triplicate growths.

Mentions: Similar to other characterized Bacteroides polysaccharide degrading systems, the xylan degrading apparatus of B. ovatus appears to be optimized to maximize intracellular breakdown, which may indicate that the bacterium adopts a ‘selfish' strategy when deconstructing the hemicellulose171819. In contrast with this selfish hypothesis is the observation that on simple xylans, such as BGX and WAX, B. ovatus was able to support the growth of Bifidobacterium adolescentis strain ATCC 15703, which utilizes simple linear and arabino-xylooligosaccharides but not xylans47 (Fig. 9a,b and Supplementary Fig. 7). The Bacteroides, however, was unable to promote the growth of the Bifidobacterium on highly complex xylans such as CX (Fig. 9c). It could be argued that this differential capacity of B. ovatus to support the growth of B. adolescentis reflects the extent to which oligosaccharides from complex (CX) and simple (BGX and WAX) xylans are released into the culture medium and are thus available to the Bifidobacterium. It should be emphasized, however, that as we show here, CX breakdown requires a suite of enzymes not associated with canonical xylan degrading systems. Indeed only a limited number of closely related species of Bacteroides appear to contain these additional enzymes (see above and Fig. 8a). Thus, the inability of B. ovatus to support growth of B. adolescentis on CX may simply reflect the fact that the Bifidobacterium lacks the necessary apparatus to utilize this complex xylan. To explore this possibility a BACOVA_03433 GH98 mutant was constructed in which the key catalytic residues of the GH98 enzyme (Glu361 and Asp467) had been replaced with alanine. The mutant (ΔGH98) lacked an active surface GH98 xylanase and was unable to cleave the backbone of CX, preventing growth on the complex GAX (Fig. 9e). The B. ovatus variant, however, retained the other components of the xylan degrading apparatus, and was thus able to grow well on CX that had been pre-digested with recombinant GH98 (Fig. 9e). Co-culture of ΔGH98 with wild-type B. ovatus on intact CX supported the growth of both strains, demonstrating that PBPs are indeed released into the culture medium by wild-type B. ovatus during growth on CX (Fig. 9f). Thus, the inability of B. adolescentis to grow on CX in the presence of B. ovatus does not reflect the release of an inadequate supply of xylan-derived PBPs, but indicates that the Bifidobacterium lacks the apparatus required to utilize these highly complex oligosaccharides. This is consistent with the finding that B. adolescentis is unable to grow on CX that had been pre-digested with either the GH98 alone or all the surface located enzymes encoded by PUL-XylL (Supplementary Fig. 7).


Glycan complexity dictates microbial resource allocation in the large intestine.

Rogowski A, Briggs JA, Mortimer JC, Tryfona T, Terrapon N, Lowe EC, Baslé A, Morland C, Day AM, Zheng H, Rogers TE, Thompson P, Hawkins AR, Yadav MP, Henrissat B, Martens EC, Dupree P, Gilbert HJ, Bolam DN - Nat Commun (2015)

The ability of other members of the microbiota to use PBPs released by B. ovatus during growth on xylan is determined by the complexity of the polysaccharide.Bacteroides ovatus (Bo) and Bifidobacterium adolescentis were co-cultured on BGX (a) WAX (b) and CX (c) and the number of CFUs of each determined at different points on the growth curve. (d) Shows the CFU ml-1 of B. ovatus alone at different phases of growth. Note, when the Bifidobacterium alone was grown on digested xylans (see Supplementary Fig. 8), the CFU ml−1 at late exponential phase (OD600 ∼1.2) was ∼8.0 × 108, indicating that ∼25% of the total xylan is used by B. adolescentis. (e) Growth of B. ovatus wild type and the ΔGH98 mutant (BACOVA_03433) on CX (0.5% w/v). Pre-digested indicates the CX was digested to completion with the GH98 xylanase prior to addition to the media. (f) Tagged strains of wild-type B. ovatus and the ΔGH98 mutant were co-cultured on CX (see panel e for growth curve). Samples were taken at different time points and qPCR with primers unique to each strain was used to determine the ratio of each in the culture. Each data point is the average and s.d. of triplicate growths.
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Related In: Results  -  Collection

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f9: The ability of other members of the microbiota to use PBPs released by B. ovatus during growth on xylan is determined by the complexity of the polysaccharide.Bacteroides ovatus (Bo) and Bifidobacterium adolescentis were co-cultured on BGX (a) WAX (b) and CX (c) and the number of CFUs of each determined at different points on the growth curve. (d) Shows the CFU ml-1 of B. ovatus alone at different phases of growth. Note, when the Bifidobacterium alone was grown on digested xylans (see Supplementary Fig. 8), the CFU ml−1 at late exponential phase (OD600 ∼1.2) was ∼8.0 × 108, indicating that ∼25% of the total xylan is used by B. adolescentis. (e) Growth of B. ovatus wild type and the ΔGH98 mutant (BACOVA_03433) on CX (0.5% w/v). Pre-digested indicates the CX was digested to completion with the GH98 xylanase prior to addition to the media. (f) Tagged strains of wild-type B. ovatus and the ΔGH98 mutant were co-cultured on CX (see panel e for growth curve). Samples were taken at different time points and qPCR with primers unique to each strain was used to determine the ratio of each in the culture. Each data point is the average and s.d. of triplicate growths.
Mentions: Similar to other characterized Bacteroides polysaccharide degrading systems, the xylan degrading apparatus of B. ovatus appears to be optimized to maximize intracellular breakdown, which may indicate that the bacterium adopts a ‘selfish' strategy when deconstructing the hemicellulose171819. In contrast with this selfish hypothesis is the observation that on simple xylans, such as BGX and WAX, B. ovatus was able to support the growth of Bifidobacterium adolescentis strain ATCC 15703, which utilizes simple linear and arabino-xylooligosaccharides but not xylans47 (Fig. 9a,b and Supplementary Fig. 7). The Bacteroides, however, was unable to promote the growth of the Bifidobacterium on highly complex xylans such as CX (Fig. 9c). It could be argued that this differential capacity of B. ovatus to support the growth of B. adolescentis reflects the extent to which oligosaccharides from complex (CX) and simple (BGX and WAX) xylans are released into the culture medium and are thus available to the Bifidobacterium. It should be emphasized, however, that as we show here, CX breakdown requires a suite of enzymes not associated with canonical xylan degrading systems. Indeed only a limited number of closely related species of Bacteroides appear to contain these additional enzymes (see above and Fig. 8a). Thus, the inability of B. ovatus to support growth of B. adolescentis on CX may simply reflect the fact that the Bifidobacterium lacks the necessary apparatus to utilize this complex xylan. To explore this possibility a BACOVA_03433 GH98 mutant was constructed in which the key catalytic residues of the GH98 enzyme (Glu361 and Asp467) had been replaced with alanine. The mutant (ΔGH98) lacked an active surface GH98 xylanase and was unable to cleave the backbone of CX, preventing growth on the complex GAX (Fig. 9e). The B. ovatus variant, however, retained the other components of the xylan degrading apparatus, and was thus able to grow well on CX that had been pre-digested with recombinant GH98 (Fig. 9e). Co-culture of ΔGH98 with wild-type B. ovatus on intact CX supported the growth of both strains, demonstrating that PBPs are indeed released into the culture medium by wild-type B. ovatus during growth on CX (Fig. 9f). Thus, the inability of B. adolescentis to grow on CX in the presence of B. ovatus does not reflect the release of an inadequate supply of xylan-derived PBPs, but indicates that the Bifidobacterium lacks the apparatus required to utilize these highly complex oligosaccharides. This is consistent with the finding that B. adolescentis is unable to grow on CX that had been pre-digested with either the GH98 alone or all the surface located enzymes encoded by PUL-XylL (Supplementary Fig. 7).

Bottom Line: We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan.Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains.Our report presents a highly complex and dynamic xylan degrading apparatus that is fine-tuned to recognize the different forms of the polysaccharide presented to the human gut microbiota.

View Article: PubMed Central - PubMed

Affiliation: Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.

ABSTRACT
The structure of the human gut microbiota is controlled primarily through the degradation of complex dietary carbohydrates, but the extent to which carbohydrate breakdown products are shared between members of the microbiota is unclear. We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan. Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains. Our report presents a highly complex and dynamic xylan degrading apparatus that is fine-tuned to recognize the different forms of the polysaccharide presented to the human gut microbiota.

No MeSH data available.


Related in: MedlinePlus