Aspergillus niger NII-08121/MTCC 7956 exhibited differences in expression of beta-glucosidase (BGL) in response to carbon sources provided in the medium. Activity staining with methyl umbelliferyl beta-D-glucopyranoside (MUG) indicated that four different isoforms of BGL were expressed when A. niger was grown under submerged fermentation with either lactose or cellulose, whereas only two were expressed when wheat bran or rice straw was used as the carbon source. Among the four isoforms of BGL expressed during lactose supplementation, two were found to retain 92% and 82% activity respectively in presence of 250 mM glucose in the MUG assay. The major beta-glucosidase (BGL1) was purified to homogeneity by electro elution from a Native PAGE gel. The purified 120 kDa protein was active at 50 degrees C and was stable for 48 h without any loss of activity. The optimum pH and temperature were 4.8 and 70 degrees C respectively. (C) 2011 Elsevier Ltd. All rights reserved.