Enhancement of heterogeneous alkaline xylanase production in pichia pastoris GS115 by chromosomal integration of the vitreoscilla hemoglobin gene

A series of strategies were applied to improve expression level of the recombinant alkaline xylanase from Bacillus pumilus G1-3 in Pichia pastoris GS115. Codon optimization of xylanase gene xynG1-3 from B. pumilus G1-3 were carried out for its heterogeneous expression in P. pastoris. The activity of xylanase encoded by the optimized gene (xynG1-3-opt) was up to 33641 U/mL, which was 37% higher than that of xylanase encoded by the wild-type (xynG1-3) gene. To further increase the expression of xynG1-3-opt, a Vitreoscilla hemoglobin (VHb) gene was integrated into the genome of the recombinant P. pastoris GS115/xynG1-3-opt. The recombinant strain GS115/xynG1-3-opt-VHb displayed higher biomass, cell viability, and xylanase activity than strain GS115/xynG1-3-opt. The maximum xylanase activity of GS115/xynG1-3-opt-VHb in a 10 L fermentor was 53280 U/mL, which was 58% higher than that of GS115/xynG1-3-opt. The induction temperature of GS115/xynG1-3- opt-VHb was optimized in a 10 L fermentor. The maximum xylanase activity reached 60280 U/mL when the induction temperature was 28 °C. The recombinant xylanase revealed optimal activity at 55 °C and pH 8.0 and retained 64% and 68% activity after incubation without substrate at 60 °C/pH 8.0 and 55 °C/pH 11.0 for 1 h, respectively. These results will greatly contribute to increasing the production of recombinant proteins in P. pastoris and improving the industrial production of the alkaline xylanase. © 2018 American Scientific Publishers.