Expression and high-yield production of extremely thermostable bacterial xylanaseB in Aspergillus niger

An extremely thermostable xylanaseB gene from hyperthermophilic bacterium Thermotoga maritima was ligated to pGHE vector and expressed in filamentous fungus Aspergillus niger. The vector was constructed using endogenous strong gla promoter, signal sequence, and pro-sequence (NVISKR). Positive transformants of the expression vector secreted XynB with thermostable characteristics, and optimal temperature >90 °C. Yield of XynB in shaking culture reached ∼0.5 g/l. Maximal enzymatic activity occurred at day 6, and was recorded as 625 U/ml fermentation supernatant in a transformant using Remazol Brilliant Blue R-D-Xylan as substrate. mRNA levels of gla, bip, and hac1 between recombinant and control strain were detected by quantitative reverse transcription PCR. None of these three genes was regulated in the strain of xynB integration, indicating that high expression of XynB did not induce unfolded protein response.