β-D-glucosidase (βG) is one of the most interesting glycosidases for the hydrolysis of glycoconjugated precursors to release active aromatic compounds in musts and wines. Oenococcus oeni strains SD-2a and 31MBR are widely used in Chinese wines to reduce the acidity. In the present study, the βG activity of the two strains was localised and partially characterised using synthetic substrate. The activity occurred in whole cells, sonication supernatants and debris, but not in the culture supernatants for both strains. Whole cells of strain SD-2a possessed greater βG activity, while strain 31MBR showed higher enzyme activity in the sonication supernatants. Strain 31MBR exhibited higher total enzyme activity than strain SD-2a. The optimum temperatures for βG from the two strains were 40ºС at pH 3.5 and 50ºС at pH 5.0, respectively. Ethanol at low concentrations had a positive effect on βG activity in both strains, while a wine-like pH (3.5) decreased the enzyme activity to a great extent. Whole cells of strain SD-2a showed the highest activity among all samples tested under wine-like conditions. Thus, strain SD-2a proved to have potential for aroma improvement in winemaking.

ABSTRACT. The putative polyketide biosynthesis (PKS) genes cos10 and pg10 were inactivated by insertion of a kanamycin-resistance gene into the genome of the geldanamycin-producing strain, Streptomyces hygroscopicus 17997. The resultant inactivation were confirmed by PCR analysis. The abilities of the PKS gene inactivation strains to produce geldanamycin were compared with the natural geldanamycinproducing strain, S. hygroscopicus 17997. The cos10-inactivated strain exhibited an unchanged ability to produce geldanamycin, but the pg10-inactivated strain can produce twice the yield of the natural strain when grown under the same conditions. We propose that there is a sub-PKS pathway in the geldanamycin-producing strain, S. hygroscopicus 17997.