Who doesn’t like blue jeans? They’re practically wrinkle-proof. The indigo dye that provides their distinctive color holds up to detergents, but ages into that soft, worn look. No wonder the average American wears jeans four days a week. No wonder it’s a $66 billion a year industry, with three billion pairs of jeans manufactured each year.
Indigo is one of the oldest dyes used for coloring textiles. Commercial synthesis of indigo dye replaced the plant source around 1900. Today, the jean industry uses about 40,000 tons of indigo a year. But there is a dark side. Industrial synthesis of indigo from petroleum is a “dirty” chemical process. Chemical production of indigo into an effective dye requires a chemical that becomes toxic to fish and some other aquatic life. And when sent to waste water treatment plants, it severely corrodes the piping.
Jeans manufacturers are interested in finding a cleaner route to produce the iconic dye. Berkeley bioengineering professor John Dueber has studied the chemical steps plants use to naturally make indigo, and he thinks he has found an environmentally green way for the industry to churn out the dye without use of the toxic compound.
When plant leaves are healthy, a chemical precursor to indigo, called indican, is caged within a sugar molecule and isolated from the rest of the cell in an organelle. Only when leaves are damaged is indican released from this compartment. The sugar protective cage is removed, allowing a chemical change that makes indigo. Green leaves turn blue.
Dueber’s lab very recently identified the plant enzyme that is essential for adding the protective sugar cage. They plan to insert its gene into bacteria. Hundreds of gallons of the harmless bacteria growing in fermentation tanks would churn out indican, held within the sugar’s molecular embrace. Later, outside the cell, a second enzyme could remove the protective glucose cage, triggering the final chemical transition to indigo. The result: environmentally cleaner jeans.
