In an experiment that could lead to mass production of strong, lightweight
silk, scientists at a Canadian biotechnology company and a United States
Army research center have spliced spider genes into cells from cows and
hamsters and induced the cells to churn out silk. The silk, grown in tissue
cultures, has been spun into threads that are comparable to those produced
The scientists are seeking to produce dragline silk, what spiders use
for the radiating spokes in their webs, a fiber that, pound for pound,
is stronger than steel but also light, elastic and easily recyclable.
"No one has been able to make fibers like this before," said Dr. Jeffrey
D. Turner, president and chief executive of the company, Nexia Biotechnologies.
"That's a huge advance in this field."
Nexia, of Vaudreuil-Dorian, Quebec, is planning to expand its silk production
to a commercial scale with goats that have been genetically altered to
secrete silk proteins in their milk. The company has bred the goats, but
they have not yet begun producing milk.
The researchers, from Nexia and the United States Army Soldier and Biological
Chemical Command in Natick, Mass., describe their work in today's issue
of the journal Science. They said they had inserted genes derived from
two species of spiders into kidney cells from baby hamsters and udder
cells from cows. The genes caused the cells to produce silk proteins,
which were collected and squeezed out a syringe into fibers.
The military is interested in silk for medical sutures and bulletproof
Dr. Cheryl Y. Hayashi, a professor of biology at the University of California
at Riverside who studies silk genes, called the research "a big breakthrough."
After decades of work, "finally, we have a way to turn these recombinant
silk proteins into something that resembles a spider silk fiber," Dr.
Scientists have long sought an artificial way to produce silk, because
spider farms are not practical; as predators, spiders do not like to live
near one other. Silk worms, which produce a fiber that is weaker than
spider silk, can be cultivated.
Researchers' efforts to produce silk until now have had limited success.
Silk protein molecules are long, and it is difficult to deduce the DNA
that produces them. It is also difficult to insert long pieces of spider
DNA into another organism's genetic code. In earlier experiments with
bacteria and yeast, scientists were able to produce only a truncated,
weaker silk protein.
The silk proteins produced by the mammal cells are longer but still
considerably shorter than proteins found in natural spider silk. In addition,
the cells produce only one of the two types of proteins commonly found
in spider silk.
Scientists do not fully understand how spiders spin their syrupy solution
of silk proteins into threads. The Nexia and Army scientists found that
giving the fibers a strong tug after they had been squirted out vastly
improved them, probably by lining up the proteins and allowing them to
interlock more tightly, like Velcro.
The synthetic silk fibers are as tough as natural fibers — a property
useful for stopping projectiles like bullets — but only about a third
as strong, meaning they can support one-third the weight before breaking.
"There's still something wrong, several things wrong," said Dr. David
P. Knight, a researcher at the University of Oxford in England.
The second silk protein was needed for strength, Dr. Knight said, and
a closer copy of the spider's spinning apparatus would produce better
results. Nonetheless, he said he was "very excited" by the advances.
Dr. Costas N. Karatzas, Nexia's vice president for research and development
and senior author of the Science paper, said the researchers would now
try to produce the second protein and try varying mixtures of the two
proteins to improve the silk.
The company's tissue cultures produce only small amounts of silk — the
experiments reported in Science generated only half an ounce.
For mass production, Nexia will turn to a herd of goats. In 2000, it
announced the birth of two genetically engineered male goats, Peter and
Webster. The researchers added to the goats' genome a silk gene designed
to switch on in the mammary glands of lactating females. They then bred
the two with females in the herd in hope that their daughters would make
silk in their milk.
The researchers verified last year that the genes were present and working
in Webster's and Peter's descendants by injecting hormones into some of
the young female offspring to induce them to lactate. The goats are now
pregnant and are expected to start producing milk naturally after they
give birth in a few months.