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Turning Bacteria into Plastic Factories

A new company has found a way to produce polymers from genetically engineered microbes that feed on sugars, replacing fossil-fuel based processes
E. coli culture



©Linda Stewart/istockphoto.com

Escherichia coli (E. coli) can give you a severe case of food poisoning or, with a little genetic engineering, a useful plastic. Scientists at San Diego–based Genomatica, Inc., have announced success in manipulating the bacteria to directly produce butanediol (BDO), a chemical compound used to make everything from spandex to car bumpers, thereby providing a more energy-efficient way of making it without oil or natural gas.

"We have engineered the organism such that it has to secrete that product in order for it to grow," says bioengineer Christophe Schilling, president and co-founder of the company, launched in 2000 to develop such chemical-producing microbes. "The interests of the organism are aligned with our interests: It grows faster when it produces more."

The E. coli can be grown in large fermentation tanks, exactly like those used to brew ethanol from corn, and have also been genetically tweaked to tolerate high concentrations of BDO in their water. "Originally, BDO was toxic to E. coli at fairly low levels but we evolved the organism such that it now tolerates the concentration we need it to grow at," Schilling says. "We grow the bacteria in sugar and water to produce the product, then purify and separate that product out of that water."

Schilling and his colleagues are attempting to produce BDO first precisely because current methods of making it require are so energy-intensive. "You need some significant energy," says chemist Herbert Exner, an executive in charge of producing BDO and other chemicals in the U.S. at Germany-based chemical giant BASF, one of the largest BDO manufacturers in the world.

In addition, BDO itself is getting more expensive, rising from below $1 to around $1.22 per pound for bulk orders, Exner says. "Natural gas and oil peaked in the last 12 months and all processes are either gas or oil related," he says. "Therefore, by nature, the raw material costs went up, so also the prices for BDO went up."

Cost will be the ultimate factor in whether this someday becomes a widely used plastic-making process; Genomatica says it's not sure how much its E. coli–produced BDO will cost, noting that results thus far have been confined to the lab.

But the company calculates that their process (even including all the energy needed to gather and transport the raw feedstocks, ranging from sugar to cellulose) requires only 32,000 British thermal units (Btus) of energy, at least 30 percent less than traditional methods. CEO Christopher Gann says the company plans to use "inexpensive, readily available, nonfood-competing renewable feedstocks." Then the E. coli can turn these waste sugars into BDO at normal pressure and temperatures under 105 degrees Fahrenheit (40 degrees Celsius), unlike the petroleum alternatives.

"This isn't an aberration where we need $250 per barrel oil to be cost competitive," Gann adds. He says the researchers so far have produced less than two pounds (a kilogram) of BDO; he expects a pilot plant to be up and running next year.

"Natural gas or oil are materials that could one day be gone," BASF's Exner says. But "major industries, such as auto manufacturers are not willing to pay a significantly higher price just because you gave your product a bio-label."

Given that three billion pounds (1.4 billion kilograms) of BDO are produced annually relatively cheaply, Genomatica has a long way to go. But the company suggests that its genetically engineered E. coli may prove a more sustainable way of producing a range of necessary plastic compounds in the future.

"We selected BDO to start with because it's a product that is relatively sophisticated in the sense of the number of steps to make it starting from oil and gas," Gann says. "In our case, we start with land and water and sunshine to end up with sugar in water to produce BDO. The important competitive advantage is less energy and a much friendlier environmental footprint."

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