Heterologous expression in Pichia pastoris and characterization of a novel GH11 xylanase from saline-alkali soil with excellent tolerance to high pH, high salt concentrations and ethanol

A GH11 xylanase gene (xyn11-1) cloned from saline-alkali soil was successfully expressed in Pichia pastoris GS115. The purified recombinant Xyn11-1 showed its maximal activity at pH 6.0, and retained more than 60.4% of activity at pH 10.0, with good pH stability. Its optimal temperature was 50 °C and it was stable after incubation for 1 h at 30 °C. Furthermore, Xyn11-1 was highly salt-tolerant, retaining more than 77.4% of activity in the presence of 0.25-4 M NaCl and displaying more than 47.2% relative activity after being incubated in the presence of 5 M NaCl at 37 °C for 10 min. In addition, 5 mM β-Mercaptoethanol, Cu2+, Co2+, and Mn2+ increased the xylanase activity by 22.3%, 8.8%, 7.1%, and 4.4%, respectively. Significantly, 93.4% and 59.8% of the optimal activity was retained in the presence of 2% and 10% (v/v) ethanol, respectively. Under optimal conditions, the Km,Vmax, and Kcat value of Xyn11-1 for beechwood xylan were 3.7 mg ml−1, 101.0 μmol min−1 mg−1 and 42.1 s−1, respectively. Xyn11-1 is a strict endo-β-1,4-xylanase, its main enzymatic products being xylotetraose and xylopentaose. Xyn11-1 is the first reported GH11 xylanase isolated from saline-alkali soil, and has excellent tolerance of high pH, high salt concentrations and ethanol, which indicates its great potential for basic research and industrial applications.