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Growing Plastic

I just polished off the last of the milk, and the plastic bottle is lying atop the other garbage in the trash bag---haunting me. It's a waste of a wonderful material, and the Fairbanks landfill (like every other landfill in the country) is filling up with the long-lasting stuff. Researchers have estimated that polyethelene foam pellets, the ubiquitous packing material, will degrade less than one percent in a century. But plastic recycling isn't available in many places, and it isn't economically competitive with new plastic, which costs only 65 cents a pound to make.

Guilt-ridden wasteful consumers like me may be saved by an unlikely superhero, a soil bacterium with the stately name of Alcaligenes eutrophus, hereinafter called Al. Just as people store energy in the form of fat, Al stores energy in the form of a biodegradable plastic, polyhydroxybutyrate or PHB. Al has found a home with Britain's Imperial Chemical Industries, where the bacteria produce enough plastic (trade name Biopol) to manufacture shampoo bottles. But Biopol costs $10 a pound, which leaves it merely a pricey novelty.

The race is on to build a better bioplastic producer: higher yield, lower cost. Researchers at the University of Michigan and the University of Virginia are moving quickly on the problem. Using the tools of genetic engineering, they've coaxed thale cress (Arabidopsis thaliana, a plant in the mustard family) to produce PHB.

To do it, they snitched some genes from Al. Al produces three enzymes that make the production of PHB possible. Each enzyme is coded for by one gene. (Think of a gene as a blueprint, and an enzyme as a house. The blueprint-gene must be present and be read before the cell can construct the enzyme-house.) Thale cress already has one of the necessary genes---gene A---so the researchers had to excise and transplant only the other two, genes B and C, from Al.

Their molecular scalpel was another enzyme, one known as a restriction endonuclease. These enzymes can cut DNA, the stuff genes are made of, but only at specific locations. To introduce the needed genes into the genome of thale cress, the researchers needed a plasmid, a circular piece of DNA found in bacteria. For this molecular surgery, they used the same restriction endonuclease to open up the plasmid that they used to cut out the genes.The cut plasmid and gene B were combined; since both gene B and the plasmid had been cut by the same molecular scalpel, they fit together like pieces of a jigsaw puzzle. The scientists repeated the process for gene C, and thus ended up with two types of plasmid.

Each genetically engineered plasmid was introduced into individual thale cress plants. The result was two plant lines, one bearing gene B and one with gene C (as well as the one both already had, gene A). Then the researchers turned to primitive technology: sex. They cross-fertilized the two different lines. The offspring of this cross breeding produced microscopic PHB granules in every cell, proof that all three genes were now working, built-in parts of the plants.

It sounds wonderful, but the work to date only amounts to a good start. Several problems remain. First, the plastic-producing plants were stunted, either as a result of a toxic effect from the plastic or as a result of the redirection of energy to plastic production instead of plant growth. Second, because the plastic was produced in small quantities in every cell, it was not easily obtained. The next step is to encourage plastic production in a harvestable portion of the plant, such as seeds. Finally, approval for sowing genetically engineered crops outside the laboratory needs to be gained, probably the biggest hurdle.

The research team predicts all these snags can be ironed out within the next 10 years. They may have an economically feasible answer to America's love of plastic and fear of overflowing landfills---and the answer to this wasteful but guilt-ridden American's prayer.