Abstract: Objective: This study aimed to isolate a strain with high alkaline xylanase activity. Methods: The target strain was isolated with xylan as the only carbon source from the paper mill sludge. The xylanase activity was determined by the 3,5-dinitrosalicylic acid (DNS) method. The strain was identified based on physiological, biochemical and 16S rRNA gene sequence analysis. Results: The optimal pH of the xylanase enzyme was 8.0, and the optimum temperature was 50 ℃. The enzyme retained 87% and 85% of its initial activity at pH 10 and 80 ℃, respectively. It proved to be highly stable to both alkali and heat. The xylanase activity of the fermentation broth of the strain was 36.85 U/mL. Conclusion: This strain was identified as Microbacterium imperiale, which could produce a thermo-alkali-stable xylanase.

Key words: alkaline xylanase, Microbacterium imperiale, characterization