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What if plants could be plastic factories?

A Massachusetts-based company is genetically modifying switchgrass to produce a polymer used to make plastics.

By Contributor / August 9, 2013

At Metabolix's greenhouse, plants produce not just glucose, but a polymer used to make plastics.

Elizabeth Barber

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Cambridge, Mass.

The greenhouse at Metabolix’s lab is full of grass. That would be unexciting, except that the 300 or so pots of switchgrass growing here have been genetically engineered to produce a kind of polymer used to make plastics.

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Metabolix, a bioplastics company founded in 1992, is one of a small group of companies and universities pushing at a new frontier in bioplastics: the genetic engineering of crops to produce plastics materials. The efforts – unique in making bioplastics not from, but in, crops – put forward a solution to the longstanding problem in bioplastics: how to make the production costs of bioplastics as cheap as, or cheaper than, oil-based plastics.

The answer, these scientists say, is in plants: What if crops, planted in droves in US farm fields, could become quiet, tiny plastics factories, churning out all the plastics we need?

But that, of course, raises another question: Is that even possible?

Bioplastics, simply put, are plastics made from renewable biomass resources as opposed to fossil fuels. Billed as a potentially cheaper and more sustainable alternative to conventional oil-produced plastics, bioplastics is a fledgling industry, and, so far, both eco-friendliness and cheapness have not been achieved in one product.

At the moment, bioplastics are often made from corn, a controversial wing of the industry, as studies have found that the fallout from the chemical use that goes into growing the corn outweighs the potential environmental benefits of using corn-based plastic. Other means of producing bioplastics, such as using bacteria to ferment sugars into polymers, remain more expensive than using fossil fuels, given the vast industrial infrastructure that supports conventional plastics-making.

In short, the big problem in bioplastics is much the same as it is throughout the entire bioindustrial field: eco-friendly, in the short term at least, is not cheap.

“It all comes down to a bottom line: Bioplastics won't ever be competitive with petro-chemical plastics if their cost is higher,” said Stevens Brumbley, a professor of molecular biology at the University of North Texas whose team works with sugar cane-derived plastics and shares funds and findings with Metabolix.

In 2001, Metabolix bought GMO giant Monsanto’s decade of research on using plants to make plastics. That year, the company began tinkering with the genome of switchgrass – a grass that Oliver Peoples, a former researcher at the Massachusetts Institute of Technology and the founder of Metabolix, says meets all the conditions for it to be deployed toward plastics production. Switchgrass is a perennial crop with a high tolerance for erratic weather, it has a high biomass and, for the moment, it does not contribute to the human food supply, meaning that it won’t be missed if fields of it are marshaled toward plastics-making.

“It just fundamentally makes sense,” said Dr. Peoples. “What’s the most abundant source of carbon? Carbon dioxide. What are the most efficient fixers of carbon dioxide? Plants.”

But what is simple in theory is, it turns out, difficult in practice. Plants are good at turning carbon dioxide into sugar, not into compounds for plastics. 

So turning the plant into a small plastics manufacturer requires some high-tech genetic engineering. That begins with modifying switchblade grass cells to have three genes that produce a compound called polyhydroxybutyrate, or PHB. Those genes are borrowed from the soil-based bacteria that are at the moment used to produce much of the PHB used in bioplastics engineering.

"In this field, being called crazy is a compliment,” said Maria Somleva, a researcher at Metabolix, as she held a warm petri dish dotted with cell cultures modified to, well, behave a bit like bacteria.

After a few weeks, those cells begin to grow a tiny, pinprick-sized sprout of green: a new plant. Once big enough, the plants are bagged and transferred to the lab’s greenhouse to be potted. There, they’ll grow into tall, pale green grass with seed-laced fibers dangling elegantly from the tips, producing in their thin stalks not just glucose but PHB.

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