Production and purification of xylanase from alkaliphilic Bacillus licheniformis and its pretreatment of eucalyptus kraft pulp

Xylanases from bacterial sources have potential applications in various industrial processes. In the present study, the effect of enzymatic pre-treatment on pulp bleaching has been investigated using purified xylanase from alkaliphilic Bacillus licheniformis strain Alk-1. The xylanase produced by present isolate while growing on wheat bran was purified to homogeneity by 5.84-fold purification with similar to 15.97% recovery by anion exchange chromatography using DEAE-cellulose. The estimated molecular weight of the xylanase was similar to 46 kDa. The optimal pH and temperature for xylanase activity were pH 9.0 and 60 degrees C, respectively. The enzyme showed good activity retention (80%) after 1 h incubation at 60 degrees C and pH 9.0. Enzyme activity was stimulated by Ca2+, Fe2+ and Mg2+ and inhibited by Cd2+, Hg2+ and Cu2+ at 2mM and 10mM conc. For xylan, the enzyme gave a Km value of 5.26 mg/mL and V-max value of 433 mu M/min/mg proteins when the reaction was carried out at 60 degrees C and pH 9.0. Pre-treatment of kraft pulp with xylanase showed 19% reduction in kappa number, compared to control pulp, after 2 h treatment. The SEM and FTIR analysis of xylanase-treated pulp revealed significant morphological and structural changes on pulp fibres. GC-MS analysis of filtrates from control and xylanase-treated pulps showed variation in the presence of different plant-derived organic compounds. The present work finds potential application in paper production by making it cleaner and ecofriendly process.