Direct selection of galactokinase-negative mutants of Candida albicans using 2-deoxy-galactose

The galactose analogue 2-deoxy-galactose (2DG) has been widely used to select for mutations in the gene encoding the galactose pathway enzyme galactokinase (GalK). We have tested the effect of 2DG on Candida albicans to see if it could be used to obtain GalK- mutants in this diploid asexual yeast. 2DG was shown to be toxic to wild-type cells. Enzyme assays demonstrated that 2DG can induce GalK as efficiently as galactose. Examination of the initial rate of galactose uptake indicated that the galactose transport system is constitutive. 2DG-resistant mutants were isolated from mutagenized cultures and shown to have very low levels of GalK activity. The potential genetic applications of this system of direct mutant selection are discussed.