Xylanase production under solid-state fermentation and its characterization by an isolated strain of Aspergillus foetidus in India

A locally isolated strain of Aspergillus foetidus MTCC 4898 was studied for xylanase (EC 3.2.1.8) production using lignocellulosic substrates under solid state fermentation. Corncobs were found as the best substrates for high yield of xylanases with poor cellulase production. The influence of various parameters such as temperature, pH, moistening agents, moisture level, nitrogen sources and pretreatment of substrates were evaluated with respect to xylanase yield, specific activity and cellulase production. Influence of nitrogen sources on protease secretion was also examined. Maximum xylanase production ( 3065 U/g) was obtained on untreated corncobs moistened with modified Mandels and Strenberg medium, pH 5.0 at 1: 5 moisture levels at 30 degrees C in 4 days of cultivation. Submerged fermentation under the same conditions gave higher yield ( 3300 U/g) in 5 days of cultivation, but productivity was less. Ammonium sulphate fractionation yielded 3.56-fold purified xylanase with 76% recovery. Optimum pH and temperature for xylanase activity were found to be 5.3 and 50 degrees C respectively. Kinetic parameters like K-m and V-max were found to be 3.58 mg/ml and 570 mu mol/mg/min. Activity of the enzyme was found to be enhanced by cystiene hydrochloride, CoCl2, xylose and Tween 80, while significantly inhibited by Hg++, Cu++ and glucose. The enzyme was found to be stable at 40 degrees C. The half life at 50 degrees C was 57.53 min. However thermostability was enhanced by glycerol, trehalose and Ca++. The crude enzyme was stable during lyophilization and could be stored at less than 0 degrees C.