Utilization of glucose and cellobiose byCandida molischiana

Abstract

Some of the factors that influence the biosynthesis of the Candida molischiana β-glucosidase were investigated. The yeast produced maximal enzyme activity when grown at 28 °C in a carbohydrate-containing complex medium (YM) in which the initial pH was adjusted to 6.0. The enzyme appeared to be produced constitutively, as activity was detected when either ethanol, glycerol, xylose, glucitol, mannitol, maltose, trehalose, cellobiose, cellodextrins, or soluble starch was used as the carbohydrate source. The presence of either glucose, mannose, or fructose (> 25 g/L) repressed β-glucosidase expression; however, C. molischiana did produce β-glucosidase when the initial glucose concentration was <25 g/L. When the yeast was grown in YM medium containing glucose plus cellobiose, diauxic utilization of the carbon sources was observed, and β-glucosidase activity was not detected until the glucose was depleted from the medium.Key words: β-glucosidase, glucose repression, fermentation, yeast.