Purification and characterization of a xylanase from Bacillus subtilis isolated from the degumming line

Xylanases catalyze the hydrolysis of xylan, a major hemicellulose component of cell wall besides cellulose in most plant species. To extract cellulose fibers, it will be invaluable to screen for more effective xylanase-producing microorganisms. In this paper a new strategy for easy screening of xylanase-producing strains from the degumming line was presented. Using this strategy, a weak-acidic, cellulase-free xylanase from Bacillus subtilis has been isolated, purified and characterized. The xylanase showed high specific activity (36,633.4 U/mg), presented stable characteristics and can be separated and purified simply, with molecular weight 23.3 kD, pI 9.63. It reached its optimal activity at pH 5.8 and 60 °C, and retained over 80% of its maximal activity after pre-incubation at temperature 60 °C or pH 4.6 ~ 6.4. Also, a two-step purification procedure based on the combination of ultrafiltration and gel filtration chromatography was introduced and described, achieving 17-fold purification with 68.11% yield.