PRODUCTION OF BETA-GLUCOSIDASE AND DIAUXIC USAGE OF SUGAR MIXTURES BYCANDIDA-MOLISCHIANA

The fermentation of cellobiose is a rare trait among yeasts. Of the 30 8 yeast species that utilize cellobiose aerobically, only 12 species f erment it, and only 2 species, Candida molischiana and Candida wickerh amii, also ferment cellodextrins. Candida molischiana produced beta-gl ucosidase activity on all carbon sources tested, except glucose, manno se, and fructose. When these sugars were added to cultures growing on cellobiose, the synthesis of beta-glucosidase ceased. However, the tot al amount of enzyme activity remained constant, indicating that the C. molischiana beta-glucosidase is catabolite repressed and not cataboli te inactivated. When grown in medium initially containing glucose plus xylose, cellobiose, maltose, mannitol, or glucitol, C. molischiana pr eferentially utilized glucose and produced little beta-glucosidase act ivity until glucose was nearly depleted from the medium. When grown in medium containing cellobiose plus either fructose or mannose, the yea st preferentially utilized the monosaccharides and produced little bet a-glucosidase activity. Candida molischiana produced beta-glucosidase and co-utilized cellobiose and xylose, maltose, or trehalose. Glucose and fructose, mannose, or trehalose were co-utilized; however, no beta -glucosidase activity was detected. Thus, the order of substrate prefe rence groups appeared to be (glucose, trehalose, fructose, mannose) > (cellobiose, maltose, xylose) > (mannitol, glucitol).