Metabolic Engineering of Saccharomyces cerevisiae for the Production of 2-Phenylethanol

Abstract

2-Phenylethanol (2-PE), a fragrance compound with rose-like odor, has been widely used in the perfumery, cosmetics, and food industry. So far, 2-PE-producing yeast strains have been developed based on the screening of natural or mutagenized strains. In this study, we report the first metabolic engineering approach for 2-PE production in Saccharomyces cerevisiae. In yeast, 2-PE can be produced from L-phenylalanine (L-Phe) degradation via Ehrlich pathway, which consists of 3 steps involving transamination to phenylpyruvate, decarboxylation to phenylacetealdehyde, and finally reduction to 2-PE. Aro9 and Aro10 act as transaminase and decarboxylase, respectively, in the degradation of aromatic amino acids. Phenylacetealdehyde can also be oxidized to phenylacetate, competing with 2-PE production. We demonstrated that Ald3 aldehyde dehydrogenase is mainly responsible for the phenylacetealdehyde oxidation, with Ald2 playing a minor role. To enhance 2-PE production, we deleted ALD3 gene and increased expression levels of ARO9 and ARO10, both by episomal overexpression and induction of the endogenous genes by overexpression of Aro80 transcription factor involved in the activation of ARO9 and ARO10 in response to the aromatic amino acids availability. The resulting strain produced 4.7 g/L 2-PE in a medium containing 10 g/L L-Phe as a sole nitrogen source. Considering the cytotoxicity of 2-PE, this production titer is almost the upper limit that can be reached in batch cultures, suggesting the great potential of this yeast strains for 2-PE production.