This is the eighth and possibly penultimate post in a series of posts about UC Berkeley's 2013 International Genetically Engineered Machine (iGEM) team. If you'd like to catch up: part 1, part 2, part 3, part 4, part 5, part 6, and part 7.
The indigo dye in your blue jeans isn't soluble in water. If it was, wearing blue jeans in the rain would be a messy experience. Indigo is chemically reduced into a soluble form ("white indigo"), exposed to pants, and then dried. The oxygen in the air converts the white indigo back into indigo dye, which fixes itself to the cotton.
We've been able to make indigo dye in bacteria for a while now, but our primary interest has been in the dyeing process - could we avoid using chemicals to make indigo soluble?
Plants have a neat trick. They have an enzyme (GT) that can stick a glucose molecule onto a precursor of indigo, turning it into indican - which is soluble. The raw material that makes indigo gets trapped as indican. Plants have another enzyme (GLU) that can remove the glucose, which quickly leads to indigo formation. (You see this in leaves of woad after they're damaged.)
Plants already do exactly what they want - they make a soluble form of indigo without reducing agents, and they can turn that back into indigo via the GLU enzyme. We designed bacteria that produced the GLU enzyme from plants and purified it. So, what would happen if we dipped two pieces of cotton into two different concentrations of indican, then added purified GLU enzyme?
Something like this.
To be sure we're actually dyeing the cotton bears, we washed them in water, detergent, ethanol, and acetone. Only the acetone removes any of the dye, and even that not so much.
We're still on the hunt for an enzyme from plants that will allow us to make indican in bacteria as well, moving the entire process of synthesizing and dyeing with indigo into the realm of synthetic biology.
If you're interested in learning the details of this project, Berkeley's iGEM wiki can be found here.
Terry D. Johnson is a Berkeley bioengineering lecturer and author who didn't do any of these experiments. You can tell because they worked. 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.