Indigo dye is useful in part because it's water insoluble. (Otherwise, your blue jeans would be white jeans after a wash.) Now that we can make indigo in bacteria, we're looking into the rest of process of dyeing fabric with it - could there be advantages to a biological approach?
Indigo must be chemically reduced into what is called "white indigo" to dissolve it. Fabric is then exposed to the white indigo. As that fabric dries, the indigo is oxidized back into indigo, staining the fabric with a water-insoluble blue. (If your chemist friend has white spots on her blue jeans, she may have been insufficiently cautious with a reducing agent.) In industry this reduction is performed chemically, though it could also be done biologically.
Perhaps more interestingly, going from indigo to white indigo to fabric might not be the only option. If you crush leaves of woad (shown), you release precursors of indigo stored in the plant, which can be converted to indigo. If we can produce these precursors in bacteria or yeast, stain fabric with the precursors, and then convert them into indigo, we may be able to avoid reducing agents and white indigo entirely.
So, we look for syn bio alternatives to an industrial process, build those alternatives, test them, and compare them to the status quo. If we can demonstrate some combination of environmental, economic, or safety advantages over how indigo dyeing is done now, that'll do.
We're currently considering several alternatives to the industrial process for woad, replacing different chemical steps with syn bio alternatives. In living systems, "chemistry" usually means "enzymes", so we're producing and testing a laundry list of enzymes that various plants use to process indigo precursors (or molecules very like indigo precursors). Several of the most promising of these enzymes have never been sequenced (though some have been analyzed in other ways). Since we need to know the DNA sequence if we want to convince bacteria or yeast to make an enzyme, our team took a field trip to UC Berkeley's Botanical Gardens and collected samples of plants that have enzymes we'd like to use. From them we're collected DNA, and we're searching those samples for sequences that code for the enzymes involved in indigo chemistry.
Next time: a biosensors update!
Terry D. Johnson is a Berkeley bioengineering lecturer and author. He has been co-advising Berkeley's iGEM team since 2008, and will be one of the lead judges for the North America region this year. His writings here do not necessarily reflect the views of iGEM HQ, Berkeley, or possibly himself, after further contemplation.