Production, purification and characterization of Bacillus sp. GRE7 xylanase and its application in eucalyptus Kraft pulp biobleaching

Abstract

Abstract Production of extracellular xylanase from Bacillus sp. GRE7 using a bench-top bioreactor and solidstate fermentation (SSF) was attempted. SSF using wheat bran as substrate and submerged cultivation using oat-spelt xylan as substrate resulted in an enzyme productivity of 3,950 IU g1 bran and 180 IU ml1, respectively. The purified enzyme had an apparent molecular weight of 42 kDa and showed optimum activity at 70C and pH 7. The enzyme was stable at 60–80C at pH 7 and pH 5–11 at 37C. Metal ions Mn2+ and Co2+ increased activity by twofold, while Cu2+ and Fe2+ reduced activity by fivefold as compared to the control. At 60C and pH 6, the Km for oat-spelt xylan was 2.23 mg ml1 and Vmax was 296.8 IU mg1 protein. In the enzymatic prebleaching of eucalyptus Kraft pulp, the release of chromophores, formation of reducing sugars and brightness was higher while the Kappa number was lower than the control with increased enzyme dosage at 30% reduction of the original chlorine dioxide usage. The thermostability, alkali- tolerance, negligible presence of cellulolytic activity, ability to improve brightness and capacity to reduce chlorine dioxide usage demonstrates the high potential of the enzyme for application in the biobleaching of Kraft pulp.