Genetic Engineering Turns
Corn Into Cloth
By Roger Dobson
LONDON - Cloth could soon be grown by bacteria. Scientists have harnessed genetically altered bacteria to eat sugar from corn and secrete the chemical needed to make polyester fibers.
Not only is it much cheaper and better for the environment than industrial chemical processes, the resulting polyester has a range of superior qualities and it can also be continually recycled.
DuPont scientists who have been working with biotechnologists claim the new material they have made will soon be used in clothing, carpets, curtains and synthetic leathers, as well as in the production of polyurethane elastomers.
The polymer polytrimethylene, known as 3GT, has better properties than traditional polyester, or 2GT. But it has been slow to come to market because of the high cost of making trimethylene glycol, or 3G, which is one of the main constituents of 3GT.
At present 3G is made by expensive chemical processes, but DuPont scientists working with Genencor International have taken a genetic engineering route that could revolutionize the £20 billion ($30 billion) a year world polyester market.
It is known that some naturally occurring yeasts convert sugar into glycerol, while other forms of bacteria can change glycerol to 3G. But no single organism has existed until now which can go the whole way and convert sugar into 3G.
DuPont and its collaborators have genetically engineered one type of bacterium by introducing genes from two others to make it do just that. Instead of converting sugar to ethanol (alcohol), it is modified to convert sugar or glucose into 3G.
The fermentation of sugars into alcohol by yeast or bacteria has been practiced for thousands of years, but it is only since the arrival of genetic engineering that has it been possible to harness biological processes for the production of other chemicals.
According to Ray Miller of DuPont, the advantage of the process is that in a single step you go from a low-cost raw material like corn starch to having a product that is normally expensive to manufacture.
"The approach we are taking is to use recombinant DNA, modify an organism using the genetic information from two naturally occurring organisms and inserting it into a third. You are then creating an organism that has in its body the genetic code that allows the necessary chemistry to occur. You have an organism that has all the enzymes needed to turn sugar into 3G. It then operates like a winery, taking sugar and excreting what we want," he says.
"The sequence of genes tells the bacteria what enzymes to produce. Once you figure out what sequence does what chemically, you can excise that piece of the genetic code and insert it into another organism. The new organism then has the trait that goes with the gene you have inserted," says Miller.
The production process starts with ordinary corn, which is milled to make a starch. The corn starch can then be converted using enzymes to a sugar commonly used for sweetening colas.
But the same sugar can also be fermented, and when it is mixed with the genetically modified bacteria it is ingested and converted into 3G. The chemical is then collected and separated from the liquor.
The bacteria carry on working and producing the chemical rather than the ethanol they would normally produce.
The chemical is then refined and spun to make the polymer for 3GT or improved polyester for clothing, home furnishings, upholstery, and fabric and carpets.
"It is very exciting for us, and apart from a natural material like cotton, this is the first bio material that will be used in the textile industry in large volume," says Miller. "The fermentation process uses no heavy metals or toxic chemicals, and the primary material is corn starch. Rather than releasing carbon dioxide into the atmosphere, the process captures it because the growing corn will absorb the gas," he says.
The 3GT polymer is resilient and can be molded or extruded. The fibers can be stretched by 15 percent.
It is also biodegradable and can be returned to its original components. Scientists believe it will be possible to recycle the material indefinitely.