Cellulase-free xylanase from Thermomyces lanuginosus: Optimization of production in submerged and solid-state culture

Abstract

Cultural conditions for the production of thermostable xylanase (EC 3.2.1.8) by the thermophilic fungus Thermomyces lanuginosus were investigated in both submerged and solid-state culture. Under submerged growth conditions in shake flasks, the C and N sources mainly influenced the enzyme yield. The xylanase of T. lanuginosus was found to be inducible by xylan containing C sources as well as by xylose. The enzyme spectrum in culture filtrates after growth on different C-sources was compared by means of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A central composite design was used to optimize the fermentation medium with respect to medium components. The medium for the optimal production (31.2 g l −1 corn cobs, 30.2 g l −1 yeast extract, and 5.0 g l −1 KH 2PO 4) yielded 36,200 nkat ml −1 within 7 days of cultivation. The production of other lignocellulolytic enzymes (β-xylosidase, β-glucosidase, acetyl esterase, and α-arabinofuranosidase) using the optimized medium was very low. The optimal pH values of all enzymes were determined. Filter paper cellulase, CMCase, β-mannosidase, and mannanase activities were absent. Solid-state cultures using corn cobs as C source were carried out with a water content of 70% and with yeast extract between 1.4 and 9.6% (w/w). The optimized medium containing 1.75% yeast extract yielded 125,000 nkat ml −1 xylanase activity (337,000 nkat g −1 dry solid) within 9 days of cultivation.