Blue jeans get their signature color from indigo, a dye. Producing that indigo releases chemicals that can pollute water and harm fish. That’s prompted scientists to seek cleaner — as in “greener” — methods. One new approach turns bacteria into micro-factories for the chemical dye. These microbes are “taught” to produce indigo using a chemical process found in living plants.
People used to make the blue dye by extracting it from plants. But as demand for the dye grew, so too did chemists’ know-how. By the late 1800s, German scientists had figured out how to synthesize indigo from chemicals in the lab. But large-scale production of the dye has its challenges. Wastes produced by the dye-making haven’t been kind to the environment.
So her team decided to equip bacteria to make indican. (With genetic engineering, researchers can introduce segments of DNA into bacteria. Hsu’s microbes now become factories that, under the new DNA’s control, make large amounts of the indigo plant’s proteins.) Later, the researchers soaked cloth with the bacteria’s indican. Then they exposed the cloth to the proper enzyme. Voilà! The fabric turned blue as the indican morphed into indigo.
However, the new approach might still pollute, Bechtold notes. One step releases indican’s sugar molecule into the wastewater. As sugar breaks down in lakes and rivers, it will feed hungry microbes. As they gobble it up and grow, they’ll need more oxygen. They’ll extract it from the dissolved oxygen present in water. As the microbes use this oxygen, there will be less for fish and other aquatic life. Depleting lakes and rivers of oxygen also creates foul smells.
But the main hurdle to using bacterial indigo will likely be efficiency. At this point the researchers recover a mere gram (a few hundredths of an ounce) of indican from a liter (about a quart) of bacterial culture. That means, Hsu explains, “We’d need about 18 liters [4.76 gallons] of media to dye one pair of jeans.”
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