Synthesis of jojoba-like wax esters in metabolically engineered strains of Saccharomyces cerevisiae

Sammanfattning: Yeast has a long-standing tradition in human history as a production organism of choice. Besides being used for the production of fermented products like bread or beer, it has also been extensively explored for the production of proteins and chemicals. In the past, yeast research in this respect was often focused on the production of biofuels as an alternative to fossil fuels to enable the independence of crude oil. However, crude oil also functions as a source for a wide range of chemicals. Some of these chemicals can be substituted by alternatives derived from plant oils, like jojoba oil. Jojoba seeds contains approximately 50% (w/w) oil, which consists mostly (up to 97%) of wax esters (WEs). Minor parts include phytosterols, triacylglycerols (TAGs) and fatty alcohols (FOHs). This makes jojoba exceptional, since plants usually accumulate TAGs as storage compounds. Jojoba oil can among other applications be used in cosmetic and personal care products as well as lubricants. Currently, around 4,000 tons/year of jojoba oil is produced, with an estimated demand of up to 200,000 tons/year. Because of this, oil produced from the jojoba plant will not be enough to meet the demand in the future, even if huge land areas in various parts of the world are planted. Therefore, jojoba oil production in modified microorganisms represents a very promising approach. In this thesis, the yeast Saccharomyces cerevisiae was explored as a production organism for jojoba-like WEs. Jojoba-like WEs are naturally derived from the fatty acid (FA) metabolism of the plant, more specifically from very long-chain monounsaturated fatty acids (VLCMUFAs) with a carbon chain length of 20/22 (C20/C22). These VLCMUFAs can be converted to FOHs by the action of fatty acyl reductases (FARs). WEs are synthesized by wax synthases (WSs), which esterify an activated FA (fatty acyl-CoA) with a FOH molecule. In this thesis, the synthesis of jojoba-like WEs in S. cerevisiae was established by making use of various enzymes derived from bacterial and plant sources as well as tuning S. cerevisiae FA metabolism towards the increased synthesis of VLCMUFAs. In this way a S. cerevisiae strain was created that produces 14.38 +/- 1.76 mg WEs/g CDW. Of these WEs, 39.2 mol% are jojoba-like diunsaturated C38:2-WEs to C42:2-WEs, with the most abundant ones being C42:2-WEs (18.3 mol% of all WE species). These are also the most abundant WEs in natural jojoba oil (46.8 mol% of all WE species).