Production of a thermostable alkali-tolerant xylanase from Bacillus circulans AB 16 grown on wheat straw

Bacillus circulans AB 16 was able to produce 50 IU/ml of xylanase, with negligible cellulase activity when grown on untreated wheat straw. The pH optimum of the crude enzyme was 6-7 with a temperature optimum of 80 degrees C. The enzyme showed high pH and thermal stability retaining 100% activity at 60 degrees C, pH 8 and 9 after 2.5 h of incubation. The residual activity at 70 degrees C after 2.5 h was 62% and 45% at pH 8 and 9, respectively. At 75 degrees C only 22.2% activity remained at pH 8 after 1 h incubation. Since Kraft pulp is alkaline this enzyme could be used for prebleaching of pulp at temperatures up to 70 degrees C without pH adjustment.