Copper homeostasis as a target to improve Saccharomyces cerevisiae tolerance to oxidative stress.

The yeast Saccharomyces cerevisiae is widely used as a cell factory for the biotechnological production of various industrial products. During these processes, yeasts meet different kinds of stressors that often cause oxidative stress and thus impair cell growth. Therefore, the development of robust strains is indispensable to improve production, yield and productivity of fermentative processes. Copper plays a key role in the response to oxidative stress, as cofactor of the cytosolic superoxide dismutase (Sod1) and being contained in metallochaperone and metallothioneines with antioxidant properties. In this work, we observed a higher naturally copper internalization in a robust S. cerevisiae strain engineered to produce the antioxidant l-ascorbic acid (L-AA), compared with the wild type strain. Therefore, we investigated the effect of the alteration of copper homeostasis on cellular stress tolerance. CTR1 and FRE1 genes, codifying for a plasma membrane high-affinity copper transporter and for a cell-surface ferric/cupric reductase, respectively, were overexpressed in both wild type and L-AA cells. Remarkably, we found that the sole FRE1 overexpression was sufficient to increase copper internalization leading to an enhanced stress tolerance toward H2O2 exposure, in both strains under investigation. These findings reveal copper homeostasis as a target for the development of robust cell factories.