DEGRADATION AND UTILIZATION OF XYLANS BY THE RUMEN ANAEROBE PREVOTELLA-BRYANTII (FORMERLY PREVOTELLA-RUMINICOLA SUBSP BREVIS) B(1)4

Freshly harvested whole cells from cultures of P. bryantii B(1)4 grown with oat spelt xylan (OSX) as an energy source showed less than 25% o f the enzyme activity against OSX, and less than 15% of the activity a gainst birchwood xylan (BWX) and carboxymethylcellutose, that was dete ctable in sonicated cell preparations. This indicates that much of thi s hydrolytic activity is either periplasmic, membrane-associated or in tracellular and may be concerned with the processing of transported ol igosaccharides. P. bryantii B(1)4 cultures were able to utilise up to 45% and 51% of the total pentose present in OSX and BWX, respectively, after 24 h, but could utilize 84% of a water-soluble fraction of BWX. Analysis of the xylan left undegraded after incubation with P. bryant ii showed that while xylose and arabinose were removed to a similar ex tent, uronic acids were utilized to a greater extent than xylose. Pred igestion of xylans with two cloned xylanases from the cellulolytic rum en anaerobe Ruminococcus flavefaciens gave Little increase in overall pentose utilization suggesting that external P. bryantii xylanases are as effective as the cloned X. flavefaciens enzymes in releasing produ cts that can be utilised by P. bryantii cells. The xylanase system of P. bryantii is able to efficiently utilise not only xylo-oligosacchari des but also larger water-soluble xylan fragments. (C) 1997 Academic P ress.