Homologue expression of a fungal endo-1,4-β-Dxylanase using submerged and solid substrate fermentations

The xyn5 gene, which encodes an endo-β-1,4-xylanase (Xyn5), in Aspergillus niger GS1 was cloned into an expression cassette under the control of constitutive glyceraldhehyde-3-phosphate dehydrogenase gene promoter. The expression system was designed to produce the recombinant enzyme containing a six-histidine peptide fused to the carboxyl end of the protein. The efficiency of Xyn5 production under submerged (SmF) and solid-state (SSF) fermentation was investigated using the homologous cotransformed A. niger AB4.1. A productivity of 17.1 U/(l·h) was estimated for SSF and 3.2 U/(l·h) for SmF calculated at peak value of enzyme titers. Recombinant Xyn5 obtained by SSF on polyurethane fiber, was purified 5.1-fold by anion exchange and immobilized metal affinity chromatography, with 35.7% recovery. The purified recombinant enzyme showed an apparent molecular weight of 30 kDa and optimal activity (522 U/mg protein) at pH 5.5 and 50°C.Key words: Aspergillus niger GS1, xylanolytic activity, solid-state fermentation, homologue expression, polyurethane fiber