Will Tomorrow's Cars Run on Yeast?

• Position: Use of ethanol

A tiny, one-celled organism that turns agricultural wastes into ethanol may be the key to providing car drivers with an inexpensive, clean-burning fuel. Nancy Ho, a molecular geneticist at Purdue University, West Lafayette, Ind., has modified the genes of a particular type of yeast so that it can convert more of the sugars found in plant matter--leftover corn stalks, tree leaves, wood chips, grass clippings, even cardboard boxes--into ethanol.

Ethanol, a form of alcohol, is a liquid fuel that can be used by itself or blended with gasoline to create gasohol. When burned, ethanol produces far less air pollution and greenhouse gases than gasoline. Currently, ethanol is produced when yeast ferments the glucose, a form of sugar, contained in food crops such as cane sugar, corn, and other starch-rich grains. However, Ho points out, these crops are expensive and in limited supply, making them too costly to produce ethanol on a large scale.

The genetically engineered yeast generates at least 30% more ethanol from a given amount of plant material than the unmodified version or any other yeast. It is supportable and does not need to be grown in special nutrients or under special conditions. The yeast can use agricultural and other organic wastes--an abundant, completely renewable domestic resource--rather than food crops, a potential benefit to farmers who could gain extra income by selling crop residues to companies that produce ethanol.

The yeast that Ho modified, called Saccharomyces, is an environmentally safe microorganism commonly used by industry to ferment glucose into ethanol. It also has been used since ancient times to make wine. Beginning in the early 1980s, researchers worldwide attempted to modify the yeast genetically so that it could ferment glucose and another plant sugar, xylose...