Identification of a broad-specificity xylosidase/arabinosidase important for xylooligosaccharide fermentation by the ruminal anaerobe Selenomonas ruminantium GA192

Strains of Selenomonas ruminantium vary considerably in their capacity to f erment xylooligosaccharides. This ability ranges from strain GA192, which c ompletely utilized xylose through xylotetraose and was able to ferment cons iderable quantities of larger oligosaccharides, to strain HD4, which used o nly the simple sugars present in the hydrolysate. The ability of S. ruminan tium GA192 to utilize xylooligosaccharides was correlated with the presence of xylosidase and arabinosidase activities. The production of these activi ties appears to be regulated in response to carbon source used for growth. Both arabinosidase and xylosidase were induced by growth on xylose or xyloo ligosaccharides, but no activity was detected in glucose-or arabinose-grown cultures. A genetic locus from S. ruminantium GA192 was cloned into Escher ichia coli JM83 that produced both xylosidase and arabinosidase activities. Analyses of crude extracts from the E. coli clone and S. ruminantium GA 19 2 by using native polyacrylamide gel electrophoresis and methylumbelliferyl substrates indicated that a single protein was responsible for both activi ties. The enzyme expressed in E. coli was capable of degrading xylooligosac charides derived from xylan. DNA sequencing of the locus demonstrated the p resence of an open reading frame that encodes for a protein of 61,174 molec ular weight.