Efficient secretion of xylanase in Escherichia coli for production of prebiotic xylooligosaccharides

Combined strategies for improving the heterologous expression of a novel xylanase from Fusarium oxysporum Fo47 in Pichia pastoris

Xylanase, an enzyme capable of hydrolyzing non-starch polysaccharides found in grain structures like wheat, has been found to improve the organizational structure of dough and thus increase its volume. In our past work, one promising xylanase FXYL derived from Fusarium oxysporum Fo47 and first expressed 779.64 U/mL activity in P. pastoris. It has shown significant potential in improving the quality of whole wheat bread, making it become a candidate for development as a new flour improver. After optimization of expression elements and gene dose, the xylanase activity of FXYL strain carrying three-copies reached 4240.92 U/mL in P. pastoris. In addition, 12 factors associated with the three stages of protein expression pathway were co-expressed individually in order in three-copies strain, and the translation factor Pab1 co-expression increased FXYL activity to 8893.53 U/mL. Nevertheless, combining the most effective or synergistic factors from three stages did not exhibit better results than co-expressing them alone. To further evaluate the industrial potential, the xylanase activity and protein concentration reached 81184.51 U/mL and 11.8 g/L in a 5 L fed-batch fermenter. These engineering strategies improved the expression of xylanase FXYL by more than 104-fold, providing valuable insights for the cost-effective industrial application of FXYL in the baking field.

Efficient secretion of an enzyme cocktail in Escherichia coli for hemicellulose degradation

The use of host to secrete several hemicellulase is a cost-effective way for hemicellulose degradation. In this study, the xylose utilization gene xylAB of Escherichia coli BL21 was knocked out, and the xylanase (N20Xyl), β-xylosidase (Xys), and feruloyl esterase (FaeLam) were co-expressed in this strain. By measuring the content of reducing sugars generated by enzymatic hydrolysis of wheat bran in the fermentation supernatant, the order of the three enzymes was screened to obtain the optimal recombinant strain of E. coli BL21/∆xylAB/pDIII-2. Subsequently, fermentation conditions including culture medium, inducer concentration, induction timing, metal ions, and glycine concentration were optimized. Then, different concentrations of wheat bran and xylan were added to the fermentation medium for degradation. The results showed that the extracellular reducing sugars content reached the highest value of 33.70 ± 0.46 g/L when 50 g/L xylan was added. Besides, the scavenging rates of hydroxyl radical by the fermentation supernatant was 81.0 ± 1.41 %, and the total antioxidant capacity reached 2.289 ± 0.55. Furthermore, it showed the growth promotion effect on different lactic acid bacteria. These results provided a basis for constructing E. coli strain to efficiently degrade hemicellulose, and the strain obtained has great potential application to transform hemicellulose into fermentable carbon source.

Characterization and application of a novel xylanase from Halolactibacillus miurensis in wholewheat bread making

The presence of arabinoxylan in wholewheat flour affects its quality significantly. Here, an efficient arabinoxylan hydrolytic enzyme, Hmxyn, from Halolactibacillus miurensis was identified and heterologously expressed in pichia pastoris. Moreover, its relevant properties, including potential application in the wholewheat bread were evaluated. Recombinant Hmxyn exhibited maximal activity at 45°C and pH 6.5, and was stable at mid-range temperature (<55°C) and pH (5.5–8.0) conditions. Hmxyn had a clear hydrolysis effect on wheat arabinoxylan in dough and caused the degradation of the water-unextractable arabinoxylan, which increased the content of wheat soluble arabinoxylan of dough. The fermentation characteristics results and microstructure analysis revealed that Hmxyn improved the organizational structure and air holding capacity of fermented dough, thus promoting the dough expansion. Baking experiments further showed that Hmxyn significantly increased specific volume- and texture-linked properties of wholewheat breads. This study indicates the application potential of Hmxyn in the preparation of wholewheat bread.