Colonies of the bacterium Escherichia coli, genetically modified to produce the dye indigo (blue). Indigo has been used for thousands of years, and was originally obtained from plants such as woad, Isatis tinctoria, then Indigofera tinctoria. Chemical synthesis was developed in the late 19th Century. It is a polluting industrial process producing toxic waste. Annual world production of indigo is about 20 million kilogrammes, mostly for the dying of cotton in the manufacture of jeans. The picture shows colonies of E. coli streaked on to an agar medium in a petri dish. The bacterium has been modified genetically by the insertion of an oxygenase gene that allows the conversion of indole into indoxyl, the precursor of indigo. The production of so-called âBiotech indigoâ is a cleaner process now working on an industrial scale, with benefits to the environment.
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