Divergence of alternative sugar preferences through modulation of the expression and activity of the Gal3 sensor in yeast

Abstract

AbstractOptimized nutrient utilization is crucial for the progression of microorganisms in competing communities. Here we investigate how different budding yeast species and ecological isolates have established divergent preferences for two alternative sugar substrates: Glucose, which is fermented preferentially by yeast, and galactose, which is alternatively used upon induction of the relevantGALmetabolic genes. We quantified the dose-dependent induction of theGAL1gene encoding the central galactokinase enzyme, and found that a very large diversification exists between different yeast ecotypes and species. The sensitivity ofGAL1induction correlates with the growth performance of the respective yeasts with the alternative sugar. We further define some of the mechanisms, which have established different glucose/galactose consumption strategies in representative yeast strains by modulating the activity of the Gal3 inducer. (1) Optimal galactose consumers, such asSaccharomyces bayanus, contain a hyperactiveGAL3promoter, sustaining highly sensitiveGAL1expression, which is not further improved upon repetitive galactose encounters. (2) Desensitized galactose consumers, such asS. cerevisiaeY12, contain a less sensitive Gal3 sensor, causing a shift of the galactose response towards higher sugar concentrations even in galactose experienced cells. (3) Galactose insensitive sugar consumers, such asS. cerevisiaeDBVPG6044, contain an interruptedGAL3gene, causing extremely reluctant galactose consumption, which however still is improved upon repeated galactose availability. In summary, different yeast strains and natural isolates have evolved galactose utilization strategies, which cover the whole range of possible sensitivities by modulating the expression and/or activity of the inducible galactose sensor Gal3.