Engineering Saccharomyces cerevisiae for synthesis of -myrcene and (E)--ocimene

Monoterpenes are among the important natural plant terpenes. Monoterpenes usually have the characteristics of volatility and strong aroma. beta-Myrcene and its isomer (E)-beta-ocimene are typical acyclic monoterpenes. They are high-value monoterpenes that have been widely applied in foods, cosmetics, and medicines. However, large-scale commercial production of beta-myrcene and (E)-beta-ocimene is restricted by their production method that mainly involves extraction from plant essential oils. Currently, an alternative synthetic route utilizing an engineered microbial platform was proposed for effective production. This study used a Saccharomyces cerevisiae strain previously constructed for squalene production as the starting strain. Farnesyl diphosphate synthase (Erg20) expression was weakened by promoter replacement and screened for optimal myrcene synthase (MS) and ocimene synthase (OS) activities. In the resulting S. cerevisiae engineered for beta-myrcene and (E)-beta-ocimene synthesis, titers of beta-myrcene and (E)-beta-ocimene were enhanced by a fusion expressing a mutant Erg20* with the obtained monoterpene synthase and optimizing the added solvent in a two-phase fermentation system. Finally, by scaling up in a 5-L fermenter, 8.12 mg/L of beta-myrcene was obtained, which was first reported in yeast, and 34.56 mg/L of (E)-beta-ocimene was obtained, which is the highest reported to date. This study provides a new synthesis route for beta-myrcene and (E)-beta-ocimene.