Biosyntheis of Bioactive Seleno-Compunds in Saccharomyces cerevisiae via Metabolic and Bioprocess Engineering

Selenium (Se) is an essential element for many organisms as it is present under the form of Se-cysteine in Se-proteins. The main sources of Se for animals are edible plants able to accumulate Se from the soil and store it under organic forms. Some of Se organic forms bioavailable for animals, such as Se-methyl-selenocysteine (SeMCys), have been proven to have cancer-preventing effects if regularly introduced into the diet. Since Se content in plants is highly susceptible to environmental factors, the intake of Se is often insufficient to result in beneficial effects. Therefore, the use of Se-enriched yeast as food supplement is made available to avoid Se shortage. The yeast Saccharomyces cerevisiae does not require Se as essential element, but is able to metabolise and accumulate Se. This work shows a study of Se-metabolism in yeast that lead to the definition of a metabolic engineering strategy and to an optimized bioprocess to increase the levels of beneficial Se-compounds in yeast. After a preliminary study on Se uptake dynamics and Se-metabolite profile in yeast, a recombinant yeast strain was generated, by introducing heterologous genes from plants belonging to Brassicaceae and Fabaceae families. Due to the delicate balance between toxic and beneficial effects of Se, the cultivation process was carefully optimized in terms of medium composition and Se feeding. The established bioprocess allowed minimizing the toxicity of Se and redirecting Se fluxes towards the biosynthesis of SeMCys at the same time.The results obtained demonstrate that the coupling of genetic engineering strategies with optimization of cultivation system is a promising approach for the establishment of a yeast cell factory for the production of yeast enriched in health promoting Se-compounds