β-glucosidases from five black Aspergillus species:: Study of their physico-chemical and biocatalytic properties

Five black Aspergillus strains (A. aculeatus, A. foetidus, A. japonicus, A. niger, and A. tubingensis) were cultivated on crude wheat arabinoxylan as the carbon source under defined pH, temperature, and oxygen conditions. Protein and beta-glucosidase content differed remarkably within the obtained culture filtrates, of which eleven beta -glucosidases were isolated. Seven beta -glucosidases were purified to apparent electrophoretic homogeneity using anion-exchange and gel-permeation chromatography. They were found to be acidic proteins and most of them appeared to be glycoproteins with a molecular mass between 93 and 142 kDa. Classification of the beta -glucosidases into four groups (I-A, I-B, II, and III) is suggested according to their physicochemical and biocatalytic properties. The major beta -glucosidases were assigned to groups I-A and I-B, the minor beta -glucosidases to groups II and III, comprising acid-tolerant and glucose-tolerant enzymes, respectively.