PRODUCTION OF HIGH-LEVEL OF CELLULASE-FREE AND THERMOSTABLE XYLANASE BY A WILD STRAIN OF THERMOMYCES-LANUGINOSUS USING BEECHWOOD XYLAN

Thermomyces lanuginosus, isolated from self-heated jute stacks in Bang ladesh, was studied for production of high level of cellulase-free the rmostable xylanase at 50-degrees-C using xylan. Optimization of the me dium composition was carried out on shake-flask level using Graeco-Lat in square technique. This increased xylanase production from 527 nkat ml-1 in the original medium to 9168-9502 nkat ml-1 in the optimized me dium under optimized culture conditions e.g. initial medium pH (6.0-6. 5), culture temperature (50-degrees-C) and time (5-6 d). The lag phase was very much shorter in the laboratory reactor compared to which exi sted in the shake cultures and 7111 nkat of xylanase activity were obt ained per ml of culture filtrate at 60 h of cultivation. With a 15 min reaction time, the optimal pH and temperature for the xylanase activi ty were at 6.5 and 65-degrees-C, respectively. The enzyme was almost s table over a broad range of pH 3-9 at 20-degrees-C, with an optimum st ability at pH 6.5. After 51 h heating at 50-degrees-C the enzyme retai ned 60%, 100% and 90% activity at pH 5.0, 6.5 and 8.0, respectively. T he crude enzyme could hydrolyse xylan effectively and in only 6 h 67.3 %, 54.0% and 49.2% saccharifications were achieved for 2%, 5% and 10% substrate levels, respectively. The principal product of hydrolysis wa s xylobiose together with smaller amounts of xylooligosaccharides (deg ree of polymerization 3-7) and xylose.