The Spool

Why Making Spider Silk Is So Tricky: The Sequel

Over the past few decades, a number of groups have tried to make spider silk via modern biotechnology techniques, but spider silk textile products still aren’t available for sale. Why not, and what are we doing differently?

Engineering a silk-producing organism neatly sidesteps the obstacles we mentioned in the previous post, but the method has its own challenges.

Researchers have gone through a menagerie of host organisms searching for the secret to spider silk production. They’ve tried using goats, modified silkworms, and microorganisms such as Salmonella and E. coli. And some of them did make silk. But no one ever achieved the holy grail of spider silk fibers: making sufficient quantities at a price reasonable enough to sell commercially.

We think we’ve cracked the code of making Microsilk™ at scale economically. Given all the attempts by other groups, you can see that this was not an easy feat.

Getting an organism to make a protein it doesn’t normally make (especially silk) is hard. Silk is a very repetitive protein, meaning that it’s made up of the same amino acids over and over again. This means that the genes that code for silk are also repetitive, which makes synthesizing the genes and getting another organism to express them difficult to do cost effectively and reproducibly.

It’s even harder to engineer an organism capable of making lots and lots of silk. Sure, the goats made silk. But how would someone raise and milk enough goats to make metric tons of silk? There isn’t enough land or milkers out there. Luckily for us, scaling up yeast fermentation is a well-studied endeavor. Just ask your favorite brewer.



It’s easier to raise lots of yeast than to raise lots of goats


Getting yeast to express silk genes and make silk proteins was only half the battle. Spider silk is a special snowflake when it comes to the protein world – which is great for its mechanical properties, but also means that it’s a really tricky protein to work with. The protein is really hard to keep stable, which we have to do in order to take it from fermented liquid protein to solid fiber form. Silk proteins evolved to go rapidly from soluble (in the spider’s gland) to insoluble state (in the fiber). Which means that spider silk can’t just be dissolved in water.

Combining all the necessary areas of expertise isn’t easy. No university has a “synthetic spider silk” major; we have an awesomely talented staff with specialties in a myriad of subjects like molecular biology, chemical engineering, protein flow and processing, fiber spinning, apparel design, product development, and marketing. Our amazing team makes our work possible, and we’ve had to make a million decisions in different areas that affect the quantities of silk we can make and its price point. It’s the merging of all these subjects that makes our work – and our team – so special.




Bolt Threads
5858 Horton St, Suite 400
Emeryville, CA 94608

(415) 325-5912
For press inquiries:
For career inquiries: