Indigo goes green

An environmentally friendly method for producing indigo dye from genetically engineered bacteria is reported in a study published online this week in Nature Chemical Biology. Indigo is widely used to give denim its characteristic blue color, and this biological approach to its synthesis and application avoids the need for harsh chemicals.

Indigo is made naturally by certain plants and has been extracted for use as a blue dye for millennia. However, modern demand for the dye requires that it be chemically synthesized on an industrial scale. This process employs multiple hazardous chemicals, which can be harmful to the environment.

As a ‘green’ approach to making indigo, John Dueber and colleagues used engineered bacteria that produce a related compound called indoxyl. Indoxyl itself is unstable, but the researchers identified an enzyme that can stabilize indoxyl by linking it to a sugar molecule. When added to bacteria, this enzyme produces indican, which can be easily isolated and kept for long-term storage. Later, at the time of dyeing, a different enzyme turns indican into the familiar indigo directly on the cloth.

The authors note that their approach to producing indigo is not yet practical on the industrial scale, but in the long term may provide a more sustainable and environmentally friendly alternative to the current chemical process.