Purification and characterization of a cellulase-free xylanase of a moderate thermophile Bacillus licheniformis A99

Two cellulase-free xylanases were secreted by a thermophile, Bacillus licheniformis A99. Of the two, the predominant one was purified to homogeneity. The enzyme was optimally active at 60 degreesC, pH 6-7.5, and had a molecular weight of about 45 KDa and isoelectric point of 7.0 +/- 0.2. The K-m (for birchwood xylan) and V-max were 3.33 mg/ml and 1.111 mmols mg(-1) protein min(-1) respectively. The half-life of the enzyme was 5 h at 60 degreesC. All cations except Hg2+ and Ag+ as well as EDTA were well tolerated and did not adversely affect xylanase activity. However, SDS inhibited the enzyme activity. The release of reducing sugars from unbleached commercial pulp sample on treatment with the enzyme indicated its potential in prebleaching of paper pulp. The enzyme caused saccharification of lignocellulosics such as wheat bran, wheat straw and sawdust. This is the first report on purification and characterization of cellulase-free xylanase from a moderate thermophile Bacillus licheniformis.