Microbial degradation of complex carbohydrates in the gut - PubMed (original) (raw)

Review

. 2012 Jul-Aug;3(4):289-306.

doi: 10.4161/gmic.19897. Epub 2012 May 10.

Affiliations

Review

Microbial degradation of complex carbohydrates in the gut

Harry J Flint et al. Gut Microbes. 2012 Jul-Aug.

Abstract

Bacteria that colonize the mammalian intestine collectively possess a far larger repertoire of degradative enzymes and metabolic capabilities than their hosts. Microbial fermentation of complex non-digestible dietary carbohydrates and host-derived glycans in the human intestine has important consequences for health. Certain dominant species, notably among the Bacteroidetes, are known to possess very large numbers of genes that encode carbohydrate active enzymes and can switch readily between different energy sources in the gut depending on availability. Nevertheless, more nutritionally specialized bacteria appear to play critical roles in the community by initiating the degradation of complex substrates such as plant cell walls, starch particles and mucin. Examples are emerging from the Firmicutes, Actinobacteria and Verrucomicrobium phyla, but more information is needed on these little studied groups. The impact of dietary carbohydrates, including prebiotics, on human health requires understanding of the complex relationship between diet composition, the gut microbiota and metabolic outputs.

PubMed Disclaimer

Figures

None

Figure 1. Major diet-derived polysaccharides and microbial carbohydrate-degrading enzyme activities. The enzyme families most associated with particular activities in gut bacteria are indicated as follows: GH, glycoside hydrolase; PL, polysaccharide lyase; CE, carbohydrate esterase; G, glucose; F, fructose; X, xylose; A, arabinose; GalU, galacturonic acid; GluU, glucuronic acid. [For details refer to the CAZY website (/

www.cazy.org/

)].

None

Figure 2. Plant cell wall structure. Diagrammatic representation of the major structural polysaccharide components of a "typical" primary plant cell wall.

None

Figure 3. Examples of cell surface organization of carbohydrate-degrading enzymes in anaerobic Gram-positive gut bacteria. A and C show the domain structures and organization of two major cell-surface anchored amylases from two human intestinal anaerobes (Numbering refers to the enzyme family (as in Figure 1) or carbohydrate binding module (CBM) family). B shows the domain structures of six examples of cellulosomal polysaccharidases from the rumen bacterium Ruminococcus flavefaciens FD1. D shows the likely organization of the cellulosome in R. flavefaciens FD1; scaE, scaB, scaA and scaC are structural proteins encoded by the sca gene cluster that interact with each-other and with the cellulosomal enzyme subunits via a series of specific, non-covalent dockerin:cohesin pairings (shown, in gray). The arrows in C and D indicate sortase-mediated anchoring to the bacterial cell wall (also indicated by cross-hatching in A).

None

Figure 4. Dominant bacterial species identified by analysis of 16S rRNA sequences in fecal samples from six individuals. Data are from Walker et al. (2011) and represent the mean of 26 fecal samples from six obese male volunteers (4, or in one case 6, samples per person) taken during a 12 week controlled dietary study. Phylotypes corresponding to the 25 most abundant cultured bacterial species, that accounted for almost 50% of all sequences, are shown in descending order of abundance on the right hand side. The gray area on the left represents the 295 additional phylotypes (both cultured and uncultured organisms) that were detected.

None

Figure 5.Bacteroides thetaiotaomicron sus system. A shows the order of genes in the sus cluster that is responsible for starch utilization in this species. B shows the inferred organization of gene products on or near the bacterial cell surface (OM outer membrane, CM cytoplasmic membrane). Starch molecules are shown as sugar chains, at various stages of hydrolysis.

None

Figure 6. Energy intake and expenditure. The diagram summarizes the potential of gut microorganisms to influence energy gain and expenditure in a mono-gastric animal such as man. The energy arising from microbial fermentation via the absorption of short chain fatty acids may be influenced by microbiota composition, but more especially by gut transit, affecting the efficiency of substrate breakdown, digestion and absorption. Other potentially important, but little understood, influences however include possible effects of microbial products on satiety and energy expenditure.

Similar articles

Cited by

References

    1. Van Soest PJ. Nutritional Ecology of the Ruminant. Second edition. 2004. Cornell Univ Press USA.
    1. Ley RE, Hamady M, Lozupone C, Turnbaugh PJ, Ramey RR, Bircher JS, et al. Evolution of mammals and their gut microbes. Science. 2008;320:1647–51. doi: 10.1126/science.1155725. - DOI - PMC - PubMed
    1. McNeil NI. The contribution of the large intestine to energy supplies in man. Am J Clin Nutr. 1984;39:338–42. - PubMed
    1. Walker AW, Ince J, Duncan SH, Webster LM, Holtrop G, Ze X, et al. Dominant and diet-responsive groups of bacteria within the human colonic microbiota. ISME J. 2011;5:220–30. doi: 10.1038/ismej.2010.118. - DOI - PMC - PubMed
    1. De Filippo C, Cavalieri D, Di Paola M, Ramazzotti M, Poullet JB, Massart S, et al. Impact of diet in shaping gut microbiota revealed by a comparative study in children from Europe and rural Africa. Proc Natl Acad Sci U S A. 2010;107:14691–6. doi: 10.1073/pnas.1005963107. - DOI - PMC - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources