Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 21, 1997
Publication Date: N/A
Technical Abstract: Xylan is an abundant polysaccharide in plant cell walls and, as such, comprises a significant portion of the diets of ruminant livestock. The enzymatic hydrolysis of xylan is accompanied by the formation of xylose, arabinose, and methyl-glucuronic acid containing oligosaccharides. These oligosaccharides can be utilized by several species of xylanolytic ruminal bacteria and Selenomonas ruminantium, a non-xylanolytic species. The objective of the current study was to study the fermentation of xylooligosaccharides by strains of S. ruminantium and examine the enzymes and genes that may be important in the utilization of xylooligosaccharides by this organism. Strains of S. ruminantium varied considerably in their capacity to ferment xylooligosaccharides. 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 arabinosidase and xylosidase wer induced by growth on xylose or xylooligosaccharides, but no activity was detected in glucose or arabinose grown cultures. A genetic locus from S. ruminantium GA192 was cloned into Escherichia coli JM83, using pUC18, that produced both xylosidase and arabinosidase activities. Analyses of crude extracts from the E. coli clone and S. ruminantium GA192, using native polyacrylamide gel electrophoresis and methylumbelliferyl substrates, indicated that a single protein was responsible for both activities. DNA sequencing of the locus demonstrated the presence of an open reading frame which encodes for a protein of 61,174 molecular weight. Attempts are underway to introduce the xylosidase/arabinosidase gene into S. ruminantium strains lacking these enzyme activities.