Biotech bugs turn indigo blue in a green way.
Jeans dyed blue by bacteria may soon be swaggering down the streets. Researchers have genetically modified bugs to churn out the indigo pigment used to stain denim. The process could be a greener rival to chemical indigo production.
Originally extracted from plants, indigo dye is now made from coal or oil, with potentially toxic by-products. Bacteria have previously been adapted as alternative indigo manufacturers, but a trace by-product renders jeans an unfashionable shade of red.
Biotech indigo starts with a chemical called tryptophan, which bacteria produce naturally. Tryptophan is ideal for conversion to indigo because it already contains the ring-structure at the core of the indigo molecule. A few chemical alterations convert tryptophan into the dye.
Bioindigo E. coli have an enzyme from another microbe engineered into them that converts trytophan into the ring-containing indigo precursor indoxyl; this spontaneously turns into indigo when exposed to air.
Weyler and his team tinkered with their E. coli so that they churned out high levels of the raw material tryptophan. The researchers also inserted a gene that cuts down production of the contaminating red pigment. The efficiency of the process still needs to be improved, however, Crabb concedes.
Before the chemical process was invented, people used plants such as woad and dyers knotweed to make indigo: soaking their leaves in water releases indigos chemical precursors. How these are converted to indigo is still a mystery. Biochemist Philip John of the University of Reading, UK is heading a project to re-introduce indigo- yielding crops into Europe as a natural alternative to chemical synthesis.
Biotech and plant production would both have to be souped-up to feed the worlds obsession with blue jeans: 16,000 tonnes of dye are made annually, almost all of which is used on denim. "Theres no other dye that will give that characteristic colour," explains John, "Its got to be indigo."
HELEN PEARSON | © Nature News Service
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