ARS | Publication request: FERMENTATION OF A BACTERIAL CELLULOSE/XYLAN COMPOSITE BY MIXED RUMINAL MICROFLORA: IMPLICATIONS FOR THE ROLE OF POLYSACCHARIDE MATRIX INTERACTIONSIN PLANT CELL WALL BIODEGRADABILITY

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 8, 2000
Publication Date: N/A

Interpretive Summary: The cell walls of forage plants provide bacteria to digest fiber, which provide feed nutrients to cattle and other ruminant animals. However, bacterial digestion of these cell walls occurs much more slowly than does the digestion of cereal grains. This poor digestibility appears to be due primarily to the presence of lignin and related structures that protect the esugar polymers from bacterial digestion. To test whether chemical interactions between the sugar polymers themselves might affect digestion independent of lignin, we grew a cellulose-producing bacterium in the presence of xylan (another sugar polymer) so that a model cell wall was produced that contained cellulose and xylan, but no lignin. Digestion experiments revealed that rumen bacteria from a cow digested this composite polymer at a rate similar to the digestion rates of the two individual sugar polymers, suggesting that the interactions among the sugar polymers do not inhibit digestion. The results provide information useful to plant scientists attempting to improve digestibility by reducing the effects of lignin and related compounds in forage plants.

Technical Abstract: Growth of the cellulose-synthesizing bacterium Acetobacter xylinum ATCC 53524 in media supplemented with 5% (w/v) glucose and 0.2% (w/v) of a water soluble, nearly linear xylan from tobacco stalks resulted in the synthesis of a highly crystalline composite that contained about 10% xylan and about 90% cellulose. The digestion of this composite by mixed ruminal microflora displayed kinetics of gas production similar to those of an unassociated mixture of the two components added in a xylan/cellulose ratio similar to that of the composite. The data suggest that intimate association of xylan and cellulose, as is typically found in plant cell walls, does not inhibit the rate of digestion of the component polysaccharides.