Development of a yeast cell factory for production of aromatic secondary metabolites

Aromatic secondary metabolites are compounds mainly synthesized by plants and fungi as a response to predators and environmental stresses. These compounds have a broad range of natural properties such as reduction of oxidative damage in cells, antibacterial effects and UV protection. Many of these properties can be useful for the treatment of different diseases and development of pharmaceutical products. The low abundance of these compounds in natural sources together with technical challenges for the extraction of these compounds from plants, open up the possibility for synthesizing aromatic secondary metabolites in cell factories. In this research project, we developed a yeast platform strain for the production of p-coumaric acid an intermediate compound for the synthesis of aromatic secondary metabolites. Subsequently, we performed a systems biology analysis of the strain and finally we developed an array of yeast strains expressing flavonoid metabolic pathways containing up to ten heterologous genes. The platform strain was capable of producing 1.93 ± 0.26 g L^-1 of p-coumaric acid in fed-batch fermentation, which is the highest titer that has been reported for a yeast cell factory so far. The systems biology analysis of the platform strain suggests that the strain has transcriptional downregulations in genes involved in the transport of amino acids and sugars, which could be a response to the stress triggered by the production of p-coumaric acid. The platform strain was capable of synthesizing six different types of flavonoids, and some of the engineered strains produced significant titers of flavonoid compounds such as kaempferol and quercetin. Moreover, for the first time, we synthesized the flavonoids liquiritigenin, resokaempferol and fisetin in yeast.