Long-Term Adaptation to the Fermentation of Galactose in Saccharomyces chevalieri

Abstract

THE dominant gene, controlling the adaptive fermentation of galactose, and the recessive gene, carried by the Carbondale stocks of Saccharomyces incapable of fermenting galactose, comprise a pair of extraordinarily stable and well-defined alleles. The non-fermenters of the Carbondale stock contain no detectable galactozymase and are incapable of fermenting galactose. Exceptional cultures called ‘long-term’ fermenters of galactose ferment galactose on duplicate tests after irregular periods of 4–30 days, while the corresponding stocks carrying the dominant allele cause fermentation within 48 hours. Mundkur and Lindegren¹ mated rapid-fermenter mutants isolated from ‘long-term’ fermenters with non-fermenters and found that the capacity for rapid fermentation segregated regularly at reduction, thus establishing the genic nature of the adaptation and the basis for the view that in the long-term fermenter a change occurs from non-fermenter to fermenter. The rapid fermentative character was retained by the original mutant and the segregant offspring after serial transfer on glucose.