Bacteria make indigo dyes more "green"

A paper published online January 9 in Nature-Chemical Biology reports an environmentally friendly method for producing indigo dyes from genetically modified bacteria. The representative blue color of denim fabric is usually from indigo. This biological method of synthesizing and applying indigo dyes avoids the need for harmful chemicals.

Natural indigo is derived from plants, and indigo has been extracted from plants for thousands of years as a blue dye. However, the demand for such dyes in modern society has led to the production of indigo by chemical synthesis on an industrial scale. This process uses a variety of hazardous chemicals that can cause damage to the environment.

John Dueber and colleagues at the University of California, Berkeley, used genetically engineered bacteria, which produce a related compound, phenol, to create a "green" way to produce indigo. Indole itself is not stable, but the researchers discovered an enzyme that stabilizes by combining it with a sugar molecule. This enzyme produces a urine blue mother in the presence of bacteria, which can be easily separated and stored for long periods of time. Later, when it is to be dyed, another enzyme directly transforms the urine blue mother into a familiar indigo on the fabric.

Researchers have suggested that their method of producing indigo is now unsuitable for industrial production, but in the long run it may provide a more sustainable and environmentally friendly alternative to current chemical production processes.