|Whitehead, Terence - Terry|
Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/1997
Publication Date: N/A
Citation: Interpretive Summary: Microbial fermentation in the forestomach (rumen) of ruminant livestock (sheep, cattle, goats, etc.) enables these animals to live on diets composed largely of fibrous plant materials or polysaccharides. Xylan is a major component of plant fiber and as such comprises a significant portion of the diets of these animals. The digestion of the xylan component of plants is incomplete and this contributes to the inefficient use of feed. Attempts to improve the utilization of xylan by ruminants will require an understanding of the metabolic activities of the microorganisms that live in the rumen and are involved in digestion of plant fiber. In the current research, we discovered that a rumen microbe produced digestive enzymes that are important to its ability to use portions of the xylan. These enzymes enable this microorganism to help others in the rumen digest xylan more completely. The information obtained will be helpful to devise strategies for manipulating the rumen to improve the conversion of feed nutrients into animal products.
Technical Abstract: Fermentation of xylooligosaccharides by strains of Selenomonas ruminantium was examined. Xylooligosaccharides were prepared by the partial hydrolysis of oat spelt xylan in dilute phosphoric acid (50 mM, 121 deg C, 15 min) and were added to a complex, yeast extract-trypticase containing medium. Strains of S. ruminantium varied considerably in their capacity to ferment xylooligosaccharides. Strains GA192, GA31, H18 and D used arabinose, xylose, and the oligosaccharides xylobiose through xylopentaose, as well as considerable quantities of larger, unidentified oligosaccharides. Other strains of S. ruminantium (HD4, HD1, 20-21a, H6a, W-21, S23, 5-1) were only able to use the simple sugars present in the substrate mixture. The ability of S. ruminantium strains to utilize xylooligosaccharides was correlated with the presence of xylosidase and arabinosidase activities. The production of these activities appears to be regulated. Both enzyme activities were induced by growth on xylooligosaccharides, but no activity was detected in glucose or arabinose grown cultures. Xylooligosaccharide fermenting strains of S. ruminantium exhibited considerable variation in substrate utilization patterns, and the assimilation of individual carbohydrate species also appeared to be regulated. Lactic, acetic, and propionic acids were the major fermentation end products detected.