Blue jeans can now be eco friendly as scientists have invented engineered bacteria that can produce indigo dye for denim. Blue jeans get their signature color from indigo dye. Producing indigo releases chemicals that can pollute water and harm fish. That’s prompted scientists to seek cleaner methods. One new approach uses bacteria to produce indigo using a chemical process found in living plants.

For centuries textile makers have been using a deep blue dye made from a plant. The plants’ leaves don’t store indigo but contain a related compound. Crushing the plants’ leaves releases the molecule. Then it’s free to react with oxygen in the air and pair with another of its kind to produce that prized indigo.

People used to make the blue dye by extracting it from plants. But as demand for the dye grew, so did chemists’ know-how. By the late 1800s, German scientists had figured out how to synthesisze indigo from chemicals in the lab. Their plant-free approach was faster and allowed for factories to make huge amounts. Today, factories churn out some 40,000 tons of indigo per year, just for blue jeans.

But this large-scale production of the dye has its challenges. Wastes produced by the dye-making haven’t been kind to the environment. Most fabric coloring takes place in water. Yet indigo dissolves poorly in water. To get around this problem, factories use chemicals called reducing agents. These chemicals convert indigo into a form that can dissolve in water. However reducing agent can hurt aquatic life.