Utah State University professor Randy Lewis is not trying to weave a tangled web, but he is pioneering the use of milk from genetically altered dairy goats to make spider silk proteins that may someday form durable artificial ligaments for people who have injured their knees or shoulders.
Until now, six different kinds of silk were produced by orb-web weaving spiders. These silk fibers have very different mechanical properties that are so effective they have changed very little over millions of years. How to synthetically develop these silks is one focus of Lewis’ research in Utah.
The transgenic goats have two key genes that allow a spider to weave their silk inserted into their genetic code. The result is goats that produce milk that contain spider silk proteins.
Once the proteins are harvested from the milk, Lewis and his team are able to spin them into fibers and into potentially useable materials.
"We are using Saanens due to their large milk production, high protein and low fat content of their milk," Lewis said. "We have 20 does, 10 kids and four bucks in the program at the moment. All of them are not transgenic as we breed the transgenic does to non-transgenic bucks, and the transgenic bucks to non-transgenic does. One major goal is to select for the best producing does, so we have been using bucks with very strong milk production pedigrees and using their offspring for the next generation of producing does."
Lewis said that, to his knowledge, Utah State University was home to the only goat herd in the world with the spider silk genes, though there may be a small number of goats left in Canada for historical reasons."
The goats are under constant surveillance to insure their well being at the USU research farm south of Logan.
"We have three research staff, four graduate students and four undergraduates for the research team and two of us double for the goats as well as two undergraduates who are highly experienced with dairy goats," Lewis said.
Professor Randy Lewis researches genetically altered dairy goats to make silk proteins from the milk.
All materials from the goats not used for research are incinerated or composted to insure they do not reach the human food chain.
The goats are milked twice a day and the other components from the milk are removed to isolate the two proteins that make spider silk.
There are two different lines of goats. The goats in each group contain one of the two proteins needed to make the silk. The proteins are extracted from the milk and then combined.
The cream is separated to remove most of the fat. The milk is passed through a micro filter which blocks the larger fat molecules and lets the smaller proteins by. A more refined filter then isolates the silk proteins.
"When we dry it, it looks like a white powder," Lewis said. It is the powder that is used to make the fiber.The two proteins are combined into a solution and pushed into a syringe.
But Lewis said a spider pulls its silk out of its spinners, so instead of using the syringe to push their silk out, the researchers pull it out of the needle. "The spiders pull it out like floss, not push it out like toothpaste," Lewis said.
Lewis, nicknamed "Spiderman" by his USU colleagues, turned to goats because leaving it to the spiders takes too long. An 11′ x 4′ spider silk tapestry made in Madagascar and displayed at the New York Museum of Natural History in 2009 was created after 80 people took four years to harvest enough silk from an estimated one million spiders.
|Testing silk proteins at the University of Utah.|
Lewis said it’s also obvious farming spiders is impossible because of the well-known tendency to eat their companions. "Scientists have known since the late 1800s that farming spiders isn’t possible—spiders tend to eat other spiders within the vicinity," he said. "They are cannibalistic and territorial. Spiders are not like silkworms, which you can throw in a box with mulberry leaves. There was no way to collect spider silk in a commercial way."
There’s also another reason. "To raise spiders and harvest the web isn’t feasible because the different types of silk in the web will be different than the one type you want," Lewis said.
There are six types of silk a spider can produce for a web. The strongest is used for the outer circles of an orb web. The spiders also use it to rappel down to the ground.
Lewis’ team thus far has managed to spin a fiber similar to the spider’s suspension line. "We’ve been able to somewhat duplicate that," Lewis said.
Lewis, a molecular biologist, has been working more than two decades with the proteins that allow spiders to spin strong, stretchy silk. It took two years of work to clone the first two spider silk genes.
The genes are transplanted into a goat egg, or embryo, using a process developed by a Canadian company, Nexia Biotechnologies Ltd. of Montreal, that went out of business in 2009.
"They put our spider silk technology in milk," Lewis said. "The goats produce the protein when they are lactating. We purify the proteins from the milk, dry it down, reconstitute it up and get the material we can spin into fibers." Goats were chosen over cows because they are friendly, of manageable size and go from birth to lactating faster than cattle. "It takes goats six months to mature," Lewis said. "In five more months they have babies and you’re getting milk."
Lewis also added the genes to E. coli bacteria, which grows rapidly, reproducing the silk protein.
This system is good because modifications can be put into place quickly, but goats allow a much larger quantity of the protein to be collected.
He has tried transgenic silk worms, but so far they have produced only a partial silk that is not as strong as the natural spider silk.
All this left the goats as his best current spider silk factories.
Lewis says he believes a day’s worth of milk from one goat could provide the silk protein needed for fiber for one single tendon or ligament replacement surgery.
Once in commercial production for medical applications, Lewis said he would expect he would not need more than 100 does, "if we can get production of both milk and spider silk proteins in the milk maximized. At this point neither is."
He sees no problem in the equipment evolving from the syringe used now to make the silk to meet the "industrialized" commercial demand.