Greener blue jeans

Greener blue jeans

10:14 AM, 22nd June 2018
John Dueber (right) and bioengineering graduate student Zach Russ examine a culture of indigo-producing E. coli bacteria.
John Dueber (right) and bioengineering graduate student Zach Russ examine a culture of indigo-producing E. coli bacteria.

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.

“We thought going back to the plants would be smart. If we can identify the enzyme the plants use to produce the sugar cage and clone its gene, we think the microbes can make large quantities of indican for dyeing jeans without the use of ‘dirty chemicals’,” Dueber said.

The process would be cleaner in another way. Current indigo production starts with petroleum. But the microbes thrive on cheap and plentiful glucose.

Grad students Tammy Hsu and Zachary Russ worked in a greenhouse last summer, planting seeds, harvesting about a pound of green leaves from a Japanese indigo plant and grinding them up. “As you grind the leaves,” Dueber said, “they turn into a blue paste because you have released indican from its sugar cage.”

Dueber’s project is supported by a five-year Bakar Fellowship. “I’m excited to be part of this fellowship that connects us with people who can help us identify exactly what we should be filing patents on, and how much proof-of-concept work should be done before we file,” he said. “My students want to move their research into the commercial world. For the next five years, they’ll be able to learn from experts who know this world. It’s a fantastic opportunity for all of us.”

The Berkeley indigo research started in 2013 as an entrant in an undergraduate competition called iGEM-the International Genetically Engineered Machines. Dueber advised the Berkeley team.

“Students want to make a difference with their research,” Dueber said. “We’re still going to focus our research on academically interesting questions, but when there are industrial applications, we want to be aware of that. We’d all like to see our indigo research lead to greener blue jeans.”

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