Enzymes to manufacture ‘green jeans’

19 June 2019

If it were not so hot on the day of the interview, Marco Fraaije would have surely worn a pair of jeans. ‘And when I give a lecture about our indigo enzymes, I always make sure to wear a pair,’ he says. A coincidence during a student project led the professor of molecular enzymology to the denim industry.

Credit: Gitane Wikimedia

Text by Anouck Vrouwe

‘The students standing in my office were all a little taken aback, because the bacteria they were using had developed a blue-black colour during the night,’ explains Marco Fraaije, Professor of Molecular Enzymology in Groningen. ‘Unexpected results like these are what makes working with enzymes so much fun. You think you know what you are searching for, but enzymes are so complex that the result is not always predictable. And so this experiment led us to the world of textile dyeing. I love it when that happens: you can learn so much from new worlds!’

World of dyes

Fraaije’s own world is that of enzymes, the catalysts of countless chemical reactions in biological cells. His research group manipulates enzymes to make them suitable for use in the industry. ‘We can use enzymes for the production of raw materials for medicines or plastics, for example. Or for the production of dyes.’

The striking blue-black colour of the bacteria turned out to be indigo, the dye used to colour denim. The students had introduced a mutation in an oxidizing enzyme so that it could process larger molecules. This mutation caused the bacteria that made the enzyme to produce indigo. ‘I knew there was a class of ferriferous enzymes that could produce indigo,’ says Fraaije, ‘but we thought the enzyme the students were working with wasn’t one of these.’


‘Indigo is an ancient dye that was also used in mummies. It’s poorly soluble in water, so it doesn’t easily wash out of your clothes,’ Fraaije continues. In the past, textile dyers extracted the raw material from plants. India was particularly famous for its indigo, which is where it got its name from.  Today the dye is mostly produced synthetically, but this production causes pollution. Fraaije calls it ‘hard chemistry’ and says that it produces a lot of waste products. Textile companies who want to go greener are now looking for alternative production methods.

In the wake of the students’ experiment, a coincidence gave the project an extra push: Fraaije mentioned the experiment as an aside during a conference ‘about something completely different’, and afterwards a representative of a major denim manufacturer came up to him. This meeting marked the start of a three-year joint research project. Funding was provided by NWO’s LIFT programme, which provides an impulse to innovative technologies.

Evolution with enzymes

The researchers started by unravelling the structure of the enzyme, while the next phase was to modify the enzyme to make it more stable and faster acting. ‘Costs are essential in industrial processes and both of these factors make the process cheaper,’ says Fraaije. He explains why the technique of modifying enzymes has improved enormously: ‘What used to take years is now done in a few months.’ Fraaije emphasizes the importance of controlled evolution, the method that won Frances Arnold a Nobel Prize for chemistry in 2018. This involves making random changes to the genes involved in the production of an enzyme, which results in countless variants of the original enzyme. ‘We select the best performing enzymes from among these variants,’ says Fraaije. The performance of an enzyme can improve enormously in only a few generations. 

The researchers also used computer simulations of the enzyme. ‘These have improved greatly too. The simulations show us what we can do to make the enzyme more stable,’ says Fraaije. The denim company contributed their knowledge of how to isolate and characterize indigo to the project.

Green jeans

The results of the project were so good that the results have been patented. ‘That means they really have confidence in the idea,’ says Fraaije. But he doesn’t dare to predict whether these enzymes will soon be producing the blue dye in his jeans. ‘It is difficult to say whether the project will be economically feasible. It is also a question of who your competition is. If that’s the existing technology, it will be hard to produce the dye for the same price. But if people start asking for ‘green jeans’, which would be nice, then it will be a different story.’ 

Source: NWO