Submitted to: United States-Japan Cooperative Program in Natural Resources
Publication Type: Proceedings
Publication Acceptance Date: 10/15/2004
Publication Date: 12/11/2004
Citation: Dyer, J.M., Shockey, J.M., Mullen, R.T., Chapital, D.C., Kuan, J.-C., and Stewart, G. (2004). Biotransformation of lipids in yeast cells: enzymatic conversion of fatty acids into omega-3 and conjugated fatty acids for potential usage as nutraceuticals. In: Proceedings of the 33rd Annual United States-Japan Cooperative Program in Natural Resources Annual Meeting, December 11, 2004, Tokyo, JA. p. 210-214. Interpretive Summary: Common baker's yeast is routinely used in many different types of food industries, including the production of baked goods and the fermentation of sugars to produce wine and beer. The yeast is also a favorite of scientists, since it is very easy to work with for genetic studies. In recent years, scientists have developed ways of modifying yeast cells such that they produce high-valued products, such as human insulin. In this manuscript, scientists at ARS describe ongoing research that focuses on the modification of yeast cells to produce high-value lipids (fat). The researchers demonstrate that yeast cells can be coaxed to take up large amounts of lipids from the growth media, and have modified the yeast cells to produce enzymes for conversion of lipid into higher valued lipid products. Fatty acids produced in yeast cells include a variety of nutritional and industrially important polyunsaturated fatty acids. Successful completion of this research will result in a process that can be used for conversion of low-cost lipids into value-added lipid products.
Technical Abstract: Common baker's yeast, Saccharomyces cerevisiae, is widely utilized for the development of metabolic engineering strategies geared towards the production of metabolites and therapeutic proteins, but has not been used to date for production of value-added lipids. Here we describe our current research in three areas that are critical for the development of a lipid metabolic engineering strategy in yeast cells: 1. Uptake of lipid substrates into yeast, 2. Enzymatic conversion of fatty acid structures, and 3. Packaging of modified fatty acids into storage oils. Yeast cells are typically unable to acquire complex lipids such as triacylglycerols (TAG) from the growth media, but here we demonstrate that inclusion of a nonspecific lipase in the growth medium can stimulate breakdown and uptake of lipid components. To circumvent the cost associated with lipase addition, yeast cells were engineered to secrete two different lipase enzymes into the growth medium. A variety of plant-derived fatty acid desaturases and conjugase enzymes were expressed in yeast cells to explore the possibility of converting exogenously acquired lipids into polyunsaturated fatty acids including linoleic (18:2delta 9cis,12cis), alpha-linolenic (18:3delta 9cis,12cis,15cis), gamma-linolenic (18:3delta 6cis,9cis,12cis), stearidonic (18:4delta 6cis,9cis,12cis,15cis) and alpha-eleostearic (18:3delta 9cis,11trans,13trans) acids. To increase the transfer of modified fatty acids into cellular storage oils, several diacylglycerol acyltransferase enzymes were cloned from the tung tree (Aleurites fordii), and one of them showed an increased propensity for transferring alpha-eleostearic acid into the storage oils of yeast cells. Collectively, these results provide a framework for the bioconversion of low-cost lipids into value added products in yeast cells.