Production of β-glucosidase and diauxic usage of sugar mixtures byCandida molischiana

Abstract

The fermentation of cellobiose is a rare trait among yeasts. Of the 308 yeast species that utilize cellobiose aerobically, only 12 species ferment it, and only 2 species, Candida molischiana and Candida wickerhamii, also ferment cellodextrins. Candida molischiana produced β-glucosidase activity on all carbon sources tested, except glucose, mannose, and fructose. When these sugars were added to cultures growing on cellobiose, the synthesis of β-glucosidase ceased. However, the total amount of enzyme activity remained constant, indicating that the C. molischiana β-glucosidase is catabolite repressed and not catabolite inactivated. When grown in medium initially containing glucose plus xylose, cellobiose, maltose, mannitol, or glucitol, C. molischiana preferentially utilized glucose and produced little β-glucosidase activity until glucose was nearly depleted from the medium. When grown in medium containing cellobiose plus either fructose or mannose, the yeast preferentially utilized the monosaccharides and produced little β-glucosidase activity. Candida molischiana produced β-glucosidase and co-utilized cellobiose and xylose, maltose, or trehalose. Glucose and fructose, mannose, or trehalose were co-utilized; however, no β-glucosidase activity was detected. Thus, the order of substrate preference groups appeared to be (glucose, trehalose, fructose, mannose) > (cellobiose, maltose, xylose) > (mannitol, glucitol).Key words: glucose repression, trehalase, diauxic utilization, yeast.