Production of jojoba seed oil in yeast
Jojoba oil, a natural oil derived from the seeds of the jojoba shrub (Simmondsia chinensis), can be used as a sustainable replacement for liquid paraffin, paraffinum liquidum, a highly refined form of mineral oil. Mineral oil is an inexpensive petrochemical byproduct made from petroleum and is commonly used in cosmetics and medicine. Its advantages are that it is colorless, odorless and that is has favorable water binding properties which make it a popular moisturizing ingredient. On the other hand, its disadvantage is that it forms an impenetrable film on the skin which can trap toxins and hinders normal skin respiration. Therefore, mineral oil can interfere with the natural moisturizing mechanism of the body. In contrast to that, natural moisturizers strengthen the skin’s natural lipid moisture barrier and protect it from the environment. When searching for alternatives to mineral oil for use in cosmetics and medicine, it is important to consider the natural composition of human sebum, a lipid-rich secretion produced by sebaceous glands to protect the skin. Human sebum is composed to 25% of wax monoesters, 41% triacylglycerols, 16% free fatty acids and 12% squalene. Based on this knowledge it is favorable to make use of natural sources that are rich in these constituents, e.g. the jojoba shrub, candelilla shrub or carnauba palm.
Jojoba is a perennial, woody shrub which is native to the semiarid regions of Southern Arizona, Southern California and Northwestern Mexico. Seeds of the jojoba plant contain approximately 50% (w/w) oil, which consists mostly (up to 97%) of wax monoesters and only to a minor extent of phytosterols, triacylglycerols and fatty alcohols. The current production of jojoba seed oil is ~ 4,000 tons/year with an estimated demand up to 200,000 tons/year. Since it will not be possible to meet this demand only with oil produced from the jojoba plant, jojoba oil production in modified (micro)organisms represents a very promising approach. Therefore, in this thesis the baker’s yeast Saccharomyces cerevisiae was investigated as a jojoba wax ester production platform. This yeast has been chosen, because it has already been extensively studied for the production of proteins and chemicals. The advantages of S. cerevisiae are that it is very efficient in fermenting sugars, shows a fast growth rate and is robust towards harsh industrial fermentation conditions. Another point making it an attractive choice is that it has a “generally recognized as safe” (GRAS) status. Moreover, since it is extensively used in industry, a broad knowledge about its metabolism has been acquired and a range of useful evolutionary and metabolic engineering tools have been developed. Naturally, S. cerevisiae mainly produces ethanol by fermenting sugars. By modifying its metabolism towards increased fatty acid synthesis, the precursors of wax esters, and introducing wax ester synthesizing enzymes from bacteria and plants, a yeast strain capable of producing jojoba-like wax esters was constructed.