Polysaccharides: Bacterial and Fungal


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

Figure 1.

The structure of the homopolysaccharides curdlan and scleroglucan.

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.

Figure 3.

The structures of gellan and related polysaccharides. Note that these polymers also contain O‐acetyl groups and other acyl substituents.

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.

Figure 5.

The structure of the exopolysaccharide from Xanthmonas campestris (xanthan). Typically the internal α‐mannosyl residue is fully acetylated but only c. 30% of the β‐mannosyl termini are ketalated.

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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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.

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Sutherland IW (1994) Structure–function relationships in microbial exopolysaccharides. Biotechnology Advances 12: 393–448.

Vinogradov EV, Petersen B and Bock K (1998) Structural analysis of the intact polysaccharide mannan from Saccharomyces cerevisiae yeast using 1H and 13C NMR spectroscopy at 750 MHz. Carbohydrate Research 307: 177–183.

Further Reading

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.

Whistler RL and BeMiller JN (eds) (1993) Industrial Gums, 3rd edn. San Diego, CA: Academic Press.

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Sutherland, Ian W(Apr 2001) Polysaccharides: Bacterial and Fungal. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000699]