Sucrose metabolism in Saccharomyces cerevisiae: towards synthetic yeasts with faster glycolytic rates for sucrose-based industrial biotechnology

Abstract

Yeast glycolysis is the central pathway to relevant biobased building blocks. It's regulation has been subject to decades of research - nevertheless engineering strategies to increase the glycolytic flux have failed. Interestingly, the glycolytic rate of native and industrial strains is higher on sucrose compared to glucose. In spite of these findings, sucrose metabolism in Saccharomyces cerevisiae has not been studied in detail and fundamental questions remain open, such as why S. cerevisiae actually can grow faster on sucrose compared to glucose? Aim of the proposed project is a systems level analysis of sucrose metabolism in these strains to understand and eventually engineer yeast glycolysis for higher rates on glucose.Sucrose metabolism in S. cerevisiae is driven by the enzyme invertase, which is coded by genes of the SUC gene family. The enzyme catalyses the hydrolysis of sucrose, allowing for the release of the monomers glucose and fructose. Substrate consumption in S. cerevisiae is characterized by a glucose repression mechanism that leads to preferred consumption of glucose, while the uptake and catabolism of the remaining sugars is repressed. Other sugars are only metabolized in the absence (respectively at low concentrations) of glucose. Thus, in principle growth on glucose should be faster than on sucrose. Interestingly, this is not the case - several 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. We aim to study nine different strains, including a S. cerevisae strain reaching a growth rate of 0.57 1/h on sucrose minimal medium. The precise mechanisms of gene regulation behind sucrose catabolism compared to glucose in S. cerevisiae have not yet been described, nor the metabolic makeup (i.e. metabolite concentrations and fluxes). In the project, we will use bioreactor cultivations under aerobic and anaerobic conditions and apply current systems biology tools: metabolomics, fluxomics and mathematical modeling to gather insights into cellular metabolism and regulation. This work aims at unravelling sucrose metabolism using a systems biology approach, i.e. we will study the physiology of different S. cerevisiae strains on sucrose and analyse the extra- and intracellular metabolite concentrations. The different hypothesis on sucrose regulation will be tested by mathematical modelling (simulation and prediction) and experimental validation, following the design-build-test cycle of systems biology. The group of Dr. Andreas Gombert has broad expertise in the physiological characterization of native and industrial yeast strains. The group of Dr. Aljoscha Wahl gained expertise in in-depth analysis of microbial metabolism, including yeast glycolysis which is also in the focus of the matching project (Yeast 3M). The project is in the center of the BIOEN as well as the BE-BASIC programs: Study of a fundamental biological phenomenon (namely metabolic regulation of glycolysis) with high impact on the engineering of industrial strains for sustainable biobased production of chemicals and fuels. (AU)