Ian W Sutherland, Edinburgh University, Edinburgh, UK
Published online: April 2001
DOI: 10.1038/npg.els.0000699
Microbial exopolysaccharides are the polysaccharides that are produced outside the cell wall by many microorganisms. Some are well-established biotechnological products that are manufactured commercially from renewable resources to provide biodegradable alternatives to traditional plant and algal gums. Others have potentially useful physical or chemical properties, while a few possess valuable biological properties.
Keywords: heteropolysaccharides; xanthan; mannan; glucan; alginate
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Figure 1. The structure of the homopolysaccharides curdlan and scleroglucan.
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Figure 2. The structure of bacterial alginates. In bacterial alginates there is no regular structure and only d-mannuronosyl residues carry O-acetyl groups; some are multiply acetylated. In Pseudomonas polymers there are only single l-glucoronosyl residues, whereas Azotobacter has block structures of either type.
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Figure 3. The structures of gellan and related polysaccharides. Note that these polymers also contain O-acetyl groups and other acyl substituents.
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Figure 4. The structure of the bacterial exopolysaccharide succinoglycan synthesized by Agrobacterium spp.; Rhizobium meliloti. A pyruvate ketal is commonly on the nonreducing terminal position and a succinyl half-ester on the subterminal position; acetyl groups are also usually present.
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Figure 5. The structure of the exopolysaccharide from Xanthmonas campestris (xanthan). Typically the internal -mannosyl residue is fully acetylated but only c. 30% of the -mannosyl termini are ketalated.
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Figure 6. Formation of isoprenoid lipid intermediates in exopolysaccharide synthesis. This results in the formation of the repeat unit of xanthan (acyl groups are added from
acetyl–CoA and phosphoenolpyruvate, respectively).
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| References | |
| Gacesa P (1998) Bacterial alginate biosynthesis – recent progress and future prospects. Microbiology 144: 1133–1143. | |
| Gonzalez JE, York GM and Walker GC (1996) Rhizobium meliloti exopolysaccharide: synthesis and symbiotic functions. Gene 179: 141–146. | |
| Robyt JF (1995) Mechanisms in the glucansucrase synthesis of polysaccharides and oligosaccharides from sucrose. Advances in Carbohydrate Chemistry and Biochemistry 51: 133–168. | |
| Seymour FR and Knapp RD (1980) Structural analysis of dextrans from strains of Leucosnostoc and related genera, that contain 3-O--d-glucosylated-d-glucopyranosyl residues at the branched points or in consecutive linear position. Carbohydrate Research 81: 105–129. | |
| Sutherland IW (1994) Structure–function relationships in microbial exopolysaccharides. Biotechnology Advances 12: 393–448. | |
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Vinogradov EV,
Petersen B and
Bock K
(1998)
Structural analysis of the intact polysaccharide mannan from Saccharomyces cerevisiae yeast using | |
| Further Reading | |
| book Sutherland IW (1990) Biotechnology of Microbial Exopolysaccharides. Cambridge, UK: Cambridge University Press. | |
| Sutherland IW (1994) Structure–function relationships in microbial exopolysaccharides. Biotechnology Advances 12: 393–448. | |
| book Whistler RL and BeMiller JN (eds) (1993) Industrial Gums, 3rd edn. San Diego, CA: Academic Press. | |
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