Isolation, purification and characterization of xylanase from Staphylococcus sp. SG-13 and its application in biobleaching of kraft pulp

A haloalkalophilic Staphylococcus sp. SG-13 produced an alkalistable xylana se in wheat bran medium. A 12-fold purification was achieved by using stand ard purification techniques. The purified xylanase exhibited a dual pH opti ma of 7.5 and 9.2. The optimum temperature for enzyme activity was 50 degre es C. The enzyme was stable at 50 degrees C for more than 4 h. The xylanase exhibited K-m and V-max values of 4 mg ml(-1), 90 mu mol min(-1) per mg fo r birchwood xylan and 7 mg ml(-1), 55 mu mol min(-1) per mg for oatspelt xy lan, respectively. The substrate binding affinity of xylanase was more for oatspelt xylan but birchwood xylan was hydrolysed more rapidly. The xylanas e activity was stimulated by Fe2+, Ni2+, Cu2+ and dithiothreitol up to 60% and was strongly inhibited in the presence of Co2+, Hg2+, Pb2+, phenyl meth ane sulphonyl fluoride, ethylenediaminetetraacetic acid, and acetic anhydri de up to 100%. The xylanase dose of 1.8 U g(-1) moisture free pulp, exhibit ed bleach boosting of kraft pulps optimally at pH 9.5-10.0 and 50 degrees C after 4 h of reaction time. Pretreatment of pulp with xylanase and its sub sequent treatment with 8% hypochlorite, reduced the kappa number by 30%, en hanced the brightness and viscosity by 11% and 1.8%, respectively, and impr oved the paper properties such as tensile strength and burst factor up to 1 0% and 17%, respectively.