RE-BUILDING THE CRABTREE PHENOTYPE IN YEAST

Our relationship with yeasts dates back thousands of years. Thanks to their fermentation capability, yeasts are everywhere: Baking, brewing and wine making. During fermentation, yeasts convert sugar rapidly to alcohol and carbon dioxide, allowing them to grow faster than other microorganisms. This feature is called the Crabtree effect. Throughout the evolution of the Crabtree effect, yeasts have undergone many complex metabolic changes. These changes, which led to a more pronounced Crabtree effect, are known; but the initial molecular mechanisms that promoted its evolution remain unresolved. We have recently shown that a single gene can trigger the Crabtree effect in yeasts, boosting their fermentation capability. In this project, I want to test whether this single gene switch can be the initial step towards a fermentative metabolism in the course of yeast evolution. It took several million years for yeasts to evolve the Crabtree feature in nature, but now the entire process can be re-built in the laboratory in a much shorter time. I will use laboratory evolution to simulate the evolution of the Crabtree effect and monitor the cells. They will be characterized, and genomes of the evolved cells will be sequenced and analysed to identify the genomic changes linked to the Crabtree effect. The findings of this project will not only broaden our knowledge on the genetic mechanisms of the Crabtree effect but also elucidate its evolutionary origins. Additionally, with the knowledge we gain in this project, it will be possible to further develop yeasts that can produce ethanol and lactic acid for industrial purposes.

RE-BUILDING THE CRABTREE PHENOTYPE IN YEAST Our relationship with yeasts dates back thousands of years. Thanks to their fermentation capability, yeasts are everywhere: Baking, brewing and wine making. During fermentation, yeasts convert sugar rapidly to alcohol and carbon dioxide, allowing them to grow faster than other microorganisms. This feature is called the Crabtree effect. Throughout the evolution of the Crabtree effect, yeasts have undergone many complex metabolic changes. These changes, which led to a more pronounced Crabtree effect, are known; but the initial molecular mechanisms that promoted its evolution remain unresolved. In this project, we created yeast strains that carry the genetic mutations occurred during the course of its evolution that contributed to the Crabtree effect. We characterized these strains and analysed their fermentation ability. We showed that multiple independent events can trigger the Crabtree effect in yeasts, boosting their fermentation capability. Our results demonstrate that either a single gene that is deregulating the central metabolism or deletions in the aerobic energy metabolism result in a Crabtree effect. Combinations of these mutations strengthens the fermentation capability. Additionally, we also characterized the functions of two genes related with the energy metabolism and showed their roles in the energy supply on different carbon sources which is linked to the Crabtree effect. The findings of this project helped us broaden our knowledge on the genetic mechanisms of the Crabtree effect and energy metabolism of yeast. Next steps include further characterization of these strains and evolve in the laboratory conditions to explore the initial mechanisms of the Crabtree effect. Additionally, with the knowledge we gain in this project, it will be possible to further develop yeasts that can produce ethanol and lactic acid for industrial purposes.