Purification and characterization of thermostable xylanase and b-xylosidase by the thermophilic bacterium Bacillus thermantarcticus.

Bacillus thermantarcticus, a thermophilic bacterium isolated from Antarctic geothermal soil near the crater ofMount Melbourne, produced extracellular xylanase (1,4-b-D-xylan xylanohydrolase; E.C. 3.2.1.8) and b-xylosidase (1,4-b-D-xylan xylohydrolase; E.C. 3.2.1.37). Each extracellular enzyme was separated by gel filtration with Sephacryl S-200 and further purified to homogeneity (119-fold for xylanase and 160- fold for b-xylosidase). The optimum temperatures were 80 oC for xylanase at pH 5.6 and 70 oC for b-xylosidase at pH 6.0. The isoelectric points and molecular masses were 4.8 and 45 kDa for xylanase and 4.2 and 150 kDa for b-xylosidase, respectively. Xylanase was stable at 60 oC for 24 h, whereas it showed a half life at 70 oC of 24 h and at 80oC for 50 min. b-xylosidase activity did not decrease after 1 h at 60oC. Km of xylanase for xylan was 1.6 mg/ml, Km of b-xylosidase for p-nitrophenyl-b-D-xylopyranoside was 0.5 mM and for o-nitrophenyl-b-D-xylopyranoside was 1.28 mM. The action of two enzymes on xylan gave only xylose.