Blue jeans: bacteria.

American teens share one fashion obsession: blue jeans. The typical U.S. consumer averages 7 pairs, says industry group Cotton Inc.

Denim may be stylish, but there's an unexpected downside: Blue dye may pollute the planet. In 2002, manufacturers produced 17,000 tons of synthetic indigo (chemically produced blue dye), mostly to color jeans. Historically, indigo was naturally extracted from the woad plant. Today the dye is usually produced from coal or oil--a process that can release toxic byproducts like cyanide into rivers and streams.

Now scientist Scott Power at Genencor International in Palo Alto, Calif., claims he's found a "green" alternative: vats of Escherichia coli bacteria (single-cell organisms). How can bugs that cause food poisoning also dye jeans blue? The key, Power says, lies in genetic engineering, in which a gene (unit of hereditary instruction) from one cell is inserted into another cell.

E. coli feed on simple sugar molecules, producing low levels of the protein tryptophan--a chemical cousin to indigo--as a product of digestion. "We use foreign genes to crank up E. coli's ability to produce tryptophan," Power says.

Genencor also added another bacterial gene to create an enzyme (protein that speeds up chemical reactions), which instantly converts tryptophan to indigo. And because the vast majority of E. coli is harmless--the bugs can't grow outside the production tanks--the process is "totally safe," says Power. Funded by Levi Strauss & Co., Genencor has produced 400,000 square yards of bacteria-dyed denim--enough to make a few thousand pairs of very eco-hip jeans.