Extracellular β-glucosidase Production by a Marine Aspergillus sydowii BTMFS 55 under Solid State Fermentation Using Statistical Experimental Design

A potential fungal strain producing extracellular beta-glucosidase enzyme was isolated from sea water and identified as Aspergillus sydowii BTMFS 55 by a molecular approach based on 28S rDNA sequence homology which showed 93% identity with already reported sequences of Aspergillus sydowii in the GenBank. A sequential optimization strategy was used to enhance the production of beta-glucosidase under solid state fermentation (SSF) with wheat bran (WB) as the growth medium. The two-level Plackett-Burman (PB) design was implemented to screen medium components that influence beta-glucosidase production and among the 11 variables, moisture content, inoculums, and peptone were identified as the most significant factors for beta-glucosidase production. The enzyme was purified by (NH4)(2)SO4 precipitation followed by ion exchange chromatography on DEAE sepharose. The enzyme was a monomeric protein with a molecular weight of similar to 95 kDa as determined by SDS-PAGE. It was optimally active at pH 5.0 and 50 degrees C. It showed high affinity towards pNPG and enzyme has a K-m and V-max of 0.67 mM and 83.3 U/mL, respectively. The enzyme was tolerant to glucose inhibition with a K-i of 17 mM. Low concentration of alcohols (10%), especially ethanol, could activate the enzyme. A considerable level of ethanol could produce from wheat bran and rice straw after 48 and 24 h, respectively, with the help of Saccharomyces cerevisiae in presence of cellulase and the purified beta-glucosidase of Aspergillus sydowii BTMFS 55. (C) KSBB