Inducible and Constitutive Formation of -Fructofuranosidase (Inulase) in Batch and Continuous Cultures of the Yeast Kluyveromyces fragilis

Abstract

Inulase production by Kluyveromyces fragilis on various fermentable and non-fermentable carbon sources was examined in carbon-limited continuous culture. Fructose and sucrose supported superior inulase yields [above 24 μmol sucrose hydrolysed min−1 (mg cell dry wt)−1 at pH 5·0, 50 °C], while some other carbon sources, including lactose, galactose, ethanol and lactate, did not stimulate inulase formation beyond basal levels. Thus fructose was identified as the primary physiological inducer. Isolation of a constitutive mutant also provided genetic evidence for the inducible nature of inulase in the wild-type. The mutant was generated spontaneously and selected in continuous culture. It produced high inulase activities in continuous culture irrespective of the carbon source. Inulase formation in the wild-type and mutant strain was further controlled by general carbon catabolite repression as suggested by enzyme yield patterns in batch and continuous culture.