In a farm in Wyoming, there a few unusual goats. From the outside, you would be unable to tell them apart from any other goats. But the Wyoming animals are special in that scientists can spin spider silk from their milk.
This may seem like a science fiction story, but it is not the product of anyone’s imagination. It is work made possible by the achievements of science and engineering, in particular by the development of technologies such as genetic engineering (genetic modification or GM, for UK readers) and its 2.0 version, synthetic biology.
Inside the DNA of every living organism, there is a set of rules that determines what the organism does and what it looks like. As biological research advanced, scientists learnt how to read and manipulate this genetic code and begun altering it by adding genetic information of an individual — typically associated to its useful features — into the code of another individual (not necessarily of the same species). Some bacteria, for example, have been genetically engineered for over 30 years to produce human insulin to treat diabetes.
Synthetic biology takes genetic engineering to another level. According to a 2008 briefing by the Parliamentary Office of Science and Technology in the UK, “established DNA research methods involve using genetic material from existing organisms,” while “synthetic biology is free of this constraint.” Some synthetic biologists use computers and laboratory chemicals to design and build biological parts, from a single gene to the entire genetic code, from scratch. Others, more closely related to established genetic engineers, re-design existing DNA building-blocks to give unnatural characteristics to existing organisms.
Dr Randy Lewis, the molecular biologist behind the silk-producing goats, is one of these re-designers who “puts pieces together” in ways natural biology could never do. His team began sequencing genes related to spider-silk production back in 1989. From studying this gene, they were able to understand better how spiders transform liquid proteins into strong silk fibres, and how the proteins’ structure is related to the incredible strength and elasticity of these fibres.
“We’re trying to alter both the strength and elasticity of the natural silks,” Lewis said in 2005 to National Geographic. “We’ve made a number of different synthetic genes based on what we found in natural silks — but altered in ways to make them even stronger and more flexible.”
To mass produce the custom-designed silk, the team needs an organism capable of making the right proteins. While they could simply bet on the natural silks and let spiders do the work themselves, these animals are, in Lewis’ words, “territorial and cannibalistic — you can’t really farm them in order to mass produce spider webs.” Goats, on the other hand, have been farmed for millennia.
Lewis — following up on work by Nexia Biotechnologies — had goats produce the silk proteins in their milk by adding the synthetic gene into their genetic code. The process is very tightly regulated so there are no harmful effects on the goats. Aside from those special proteins in their milk, the Wyoming animals are perfectly normal.
“When the goats have kids, and they start lactating, we collect the milk, and we can purify that spider silk protein in much, much higher quantities,” Lewis said to Science Nation, a US National Science Foundation publication. After filtering the proteins from the milk, they are exposed to the air to solidify and then wound onto a roller.
Because spiders have had 400 million years of evolution to perfect their weaving skills, and Lewis’ team is only starting, the custom-designed, goat-produced silks are not yet up to standard with their natural counterparts. But they are already stronger than steel and Kevlar — the material used in bulletproof vests — and have elasticities as great as rubber.
Once “spider-goat” silk is ready for mass production, the applications include artificial ligaments and tendons, strong sutures for surgery, and airbags. The US military, which is funding Lewis work, is interested in the silk for other uses such as light-weight bulletproof vests and parachute cables, as well as to repair bones of wounded soldiers.
Applications like these are typically what turns people’s attentions away from the possibly disconcerting fact that biologists are capable of giving goats an unnatural function. Similarly, the vast uses of the more extreme form of synthetic biology — create a new organism from scratch — are what drives research in this area, despite ethical objections by some groups. From producing vast quantities of biofuel from renewable sources to creating cells capable of regenerating human tissue, the possibilities brought about by synthetic biology are endless.
This post was inspired by a promotional video on a forthcoming documentary on synthetic biology (which I found out about through Carl Zimmer’s blog). The film promises to explore the science behind this technology and its applications, and “it also raises questions about how life is defined, where ethical boundaries ought to be established, and how controllable or wild nature really is,” according to its producers. It should be interesting!
On another note, this was my first post on molecular biology, an area I’m unfamiliar with. If you have any comments, corrections or suggestions to the text, I would be happy to hear from you. Use the comments box below or write to dinnerpartyscience[at]gmail.com.