Utility of co-expressed alkali-tolerant endoglucanase and xylanase in ameliorating wheat straw chemical pulp properties

Because of the inferior properties of wheat straw pulp compared with wood pulp, wheat straw pulp needs to be ameliorated to meet the requirements of high-grade paper production. Enzymatic treatment with cellulase and/or xylanase is recognized as an environmentally friendly and effective method for pulp modification; however, an improper enzyme system and low enzyme activity in alkaline pH are still the main obstacles to the industrial application of the enzymes. In this study, we co-expressed alkali-tolerant endoglucanase (EG) and xylanase in Bacillus subtilis Y106-WT and successfully produced alkali-tolerant enzymes that simultaneously contained high EG and xylanase activity, but little FPA and cellobiohydrolase (CBH) activity, i.e., the activities of EG, xylanase, FPA and CBH of the crude enzyme from the fermentation liquor were 8.20, 60.40, 0.12 and 0.02 IU/ml, respectively, after 64 h of fermentation. Compared to the control, the pulp brightness, breaking length, burst index and tear index of wheat straw chemical pulp increased by 2.0% ISO, 8.7%, 16.6% and 9.3%, respectively, and the beating degree decreased by 15% after treatment using the recombinant enzyme with 0.20 IU/ml EG and 1.5 IU/ml xylanase. The synergistic effect between endoglucanase and xylanase occurred during the enzymatic treatment. The possible mechanism of pulp modification was also discussed.