Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 3, 1995
Publication Date: N/A
Interpretive Summary: Feedstuffs (forages and grains) consumed by ruminant livestock like cattle, sheep and goats contain large amounts of the dietary fiber. Because they are unable to digest dietary fiber themselves, these animals are dependent on the microorganisms in their forestomach (rumen) to breakdown the fiber portion of their diets. Many different microorganisms work together to accomplish this activity, and no single species is totally responsible for this function. Because the nutrition of the animal is intimately linked to the activity of these microorganisms, we undertook the current work to try to understand how two species of ruminal bacteria interact in the digestion of one dietary fiber called xylan. We found that one species was very active in the initial degradation of xylan while the second organism was effective at using the partially degraded pieces left by the first. Certain types of breakdown products were more poorly used than others, and future studies of these materials may help us understand why dietary fiber is sometimes inefficiently used by ruminant livestock. This information will be useful for developing methods to improve feedstuff digestion and decrease feed costs.
Technical Abstract: The degradation and utilization of xylan by cocultures of Butyrivibrio fibrisolvens and Selenomonas ruminantium was studied. Cultures were grown anaerobically in complex medium containing oat spelt xylan, and the digestion of xylan and the generation and subsequent utilization of xylooligosaccharide intermediates was monitored over time. Monocultures of fB. fibrisolvens confirmed that this species rapidly degraded oat spelt xylan and a pool of extracellular degradation intermediates composed of low molecular weight xylooligosaccharides (xylobiose through xylopentaose, and larger, unidentified oligomers) accumulated in these cultures. The ability of S. ruminantium to utilize the products of xylanolysis by B. fibrisolvens was demonstrated by its ability to grow on xylan that had first been digested by the extracellular xylanolytic enzymes of B. fibrisolvens. Although enzymatic hydrolysis converted the xylan to soluble products, this salone was not sufficient to assure complete utilization by S. ruminantium and considerable quantities of oligosaccharides remained following growth. Stable xylan utilizing cocultures of S. ruminantium and B. fibrisolvens were established and the utilization of xylan monitored. Despite the presence of an oligosaccharide fermenting organism, accumulations of acid-alcohol soluble products were still noted; however, the composition of carbohydrates present in these cultures differed from that when B. fibrisolvens was cultivated alone. Residual carbohydrates present at various times during growth were of higher average Dp (degree of polymerization) in cocultures than in cultures of B. fibrisolvens alone. Structural characterization of these residual products may help define the limitations on the assimilation xylooligosaccharides by ruminal bacteria.