Engineer baker's yeast to consume plant fats.

Common baker's yeast, Saccharomyces cerevisiae, is best known for helping ferment beer and leaven bread. The most well-known and commercially significant yeasts are the related species and strains of S. cerevisiae. These organisms have long been utilized to ferment the sugars of rice, wheat, barley and corn to produce alcoholic beverages, and in the baking industry to raise dough. S. cerevisiae is commonly used as baker's yeast and for fermentation. Yeast is often taken as a vitamin supplement because it has 50% protein content and is a rich source of B vitamins, niacin and folic acid.

USDA-ARS scientists at the Southern Regional Research Center (SRRC, 1100 Robert E. Lee Blvd., P.O. Box 19687, New Orleans, LA 70179) are expanding the applications for baker's yeast. Investigators have altered the yeast's metabolism with plant genes for converting vegetable oil fats (lipids) into value-added byproducts.

Eventually, harnessing the yeast's metabolism on an industrial scale could help develop new applications for oilseed crops, such as soybeans, cotton and linseed. Ordinarily, baker's yeast has little need for lipids except to reinforce cell walls. It's a diet of sugars and carbohydrates that really gets the yeast going, producing the carbon dioxide and alcohol that bakers and brewers so desire.

But when modified with desaturase from plants, including Arabidopis, and then fed a diet of vegetable oil fatty acids, the altered yeast's lipid storage capability increases up to sevenfold. Depending on which desaturases are activated, and the growth conditions scientists create, the yeast's metabolism converts the lipids into valuable byproducts, such as alpha eleostearic acid, which is a main tung oil component, and alpha linolenic acid. The latter byproduct is an omega 3 fatty acid that's been shown to protect against heart disease and cancer.

Refining the procedures further should allow for larger-scale production of these lipid compounds in yeasts. For tung oil, this eventually could mean a way to supplement U.S. imports from China and South America. Amid fluctuating prices and quality, such imports supply most of the 1 million pounds of tung oil now used in U.S. paints, resins, inks and wood finishes.

Further information. John Dyer; phone: [phone]; fax: [phone]; email: [e-mail].