Constitutive expression of the Trichoderma reesei β-1,4-xylanase gene (xyn2) and the β-1,4-endoglucanase gene (egI) in Aspergillus niger in molasses and defined glucose media
The xylanase II (xyn2)- and endoglucanase I (egI)-encoding regions of Trichoderma reesei QM6a were successfully expressed in Aspergillus niger D15 under the transcriptional control of the glyceraldehyde-6-phosphate dehydrogenase (gpd) promoter from A. niger and the glaA terminator of Aspergillus awamori. A stable xyn2 transformant produced β-xylanase activity of 8,000 nkat/ml and 5,000 nkat/ml in shake-flask cultures containing defined or 20% (v/v) molasses medium, respectively. The recombinant Xyn2 enzyme expressed highest activity at pH 5-6 and 50-60°C and retained more than 75% of its activity after 3 h of incubation at 50°C. A stable egI transformant produced endo-β-1,4-glucanase activity of 2,300 nkat/ml in shake-flask cultures containing defined media and about half the activity in 20% molasses medium. Maximum endoglucanase activity was obtained at pH 5 and 60°C. Both Xyn2 and EgI retained >80% activity after incubation at 50°C for 3 h. The heterologous Xyn2 and EgI represent a significant portion of the total extracellular proteins produced.