Why does not Saccharomyces cerevisiae grow faster on glucose than on sucrose?

Abstract

Sucrose holds a promising role as an alternative raw material to fossil fuels for goods manufacturing in industrial fields such as chemical and liquid fuels, particularly owing its low cost and high energy content. Sucrose metabolism in Saccharomyces cerevisiae is driven by the enzyme invertase - which is coded by genes of the SUC gene family - that catalyzes the hydrolysis of this disaccharide, allowing for the release of the monomers glucose and fructose. In S. cerevisiae, a glucose repression mechanism leads to a first glucose utilization, the remaining sugars being only metabolized in the absence or low concentrations of this monosaccharide. The yeast S. cerevisiae is currently the most largely employed microorganism in the fermentation industry due to its well-known biochemical features. In spite of these aspects, sucrose metabolism in S. cerevisiae is an underresearched topic and some fundamental questions remain open, such as "Why do S. cerevisiae strains do not grow faster on glucose than on sucrose?". In principle, this should happen, since glucose metabolism is simpler than that of sucrose. Nevertheless, some previous studies on sucrose utilization by S. cerevisiae report higher specific growth rate of this yeast on sucrose, when compared to the growth on glucose. On the one hand, the majority of those studies used strains adapted during many generations, which could compromise the interpretation of results. On the other hand, the precise mechanisms of gene regulation behind sucrose catabolism in Saccharomyces cerevisiae have not yet been explained. This work aims at addressing these issues by providing a quantitative analysis of the physiology of different S. cerevisiae strains on sucrose, as well as an investigation on the levels of expression of possible genes involved in regulation by sucrose.