Production and Properties of Xylan-Degrading Enzymes from Cellulomonas uda

Xylan degradation and production of beta-xylanase and beta-xylosidase activities were studied in cultures of Cellulomonas uda grown on purified xylan from birchwood. beta-Xylanase activity was found to be associated with the cells, although in various degrees. The formation of beta-xylanase activity was induced by xylotriose and repressed by xylose. beta-Xylosidase activity was cell bound. Both constitutive and inducible beta-xylosidase activities were suggested. beta-Xylanase and beta-xylosidase activities were inhibited competitively by xylose. beta-Xylanase activity had a pronounced optimum pH of 5.8, whereas the optimum pH of beta-xylosidase activity ranged from 5.4 to 6.1. The major products of xylan degradation by a crude preparation of beta-xylanase activity, in decreasing order of amount, were xylobiose, xylotriose, xylose, and small amounts of xylotetraose. This pattern suggests that beta-xylanase activity secreted by C. uda is of the endosplitting type. Supernatants of cultures grown on cellulose showed not only beta-glucanase but also beta-xylanase activity. The latter could be attributed to an endo-1,4-beta-glucanase activity which had a low beta-xylanase activity.