Cloning, expression and characterization of a novel salt-tolerant xylanase from Bacillus sp. SN5

A xylanase gene (xyn10A) was cloned from Bacillus sp. SN5 and expressed in Escherichia coli. It encoded a 348-residue polypeptide of ~45 kDa. The deduced amino acid sequence had 68 % identity with the endo-1,4-beta-xylanase from Paenibacillus lactis 154 that belonged to family 10 of the glycoside hydrolases. Purified recombinant Xyn10A had maximum activity at 40 °C and pH 7.0, with the specific activity of 105 U/mg and a Km of 0.6 mg/ml for beechwood xylan. Xyn10A retained more than 80 % activity between 25 and 45 °C and 29 % activity at 5 °C. It exhibited the highest activity (134 %) in 0.5 M NaCl and still retained 90 % activity in 2.5 M NaCl. It retained about 87 % activity after incubation in 2 M NaCl for 24 h. The cold-active and halo-tolerant properties of Xyn10A make it promising for application in the food industry, especially in the processing of saline food and sea food.