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Engineered E. coli produce styrene from glucose

Engineers at Arizona State University have engineered E. coli to produce the commodity petrochemical styrene—a synthetic chemical derived from petroleum and natural gas products that is used worldwide in the manufacture of products such as rubber, plastic, insulation, fiberglass, pipes, automobile parts, food containers, and carpet backing—from glucose. The styrene biosynthesis pathway was constructed using genes from plants, yeast, and bacteria.

Here we demonstrate how, through the de novo design and development of a novel metabolic pathway, styrene can alternatively be synthesized from renewable substrates such as glucose. The conversion of endogenously synthesized l-phenylalanine to styrene was achieved by the co-expression of phenylalanine ammonia lyase and trans-cinnamate decarboxylase.

Candidate isoenzymes for each step were screened from bacterial, yeast, and plant genetic sources. Finally, over-expression of PAL2 from Arabidopsis thaliana and FDC1 from Saccharomyces cerevisiae (originally classified as ferulate decarboxylase) in an l-phenylalanine over-producing Escherichia coli host led to the accumulation of up to 260 mg/L in shake flask cultures. Achievable titers already approach the styrene toxicity threshold (determined as 300 mg/L). To the best of our knowledge, this is the first report of microbial styrene production from sustainable feedstocks.

—McKenna and Nielsen

Conventional Production (per RoC)
There are two commercially viable methods of producing styrene. The most common process, which accounts for >90% of total world styrene production, involves catalytic dehydrogenation of ethylbenzene.
The second process involves oxidation of ethylbenzene to its peroxide, which is then reacted with propylene to produce propylene oxide and a-methylphenyl carbinol. The carbinol is then dehydrated to produce styrene.
US production of styrene has risen fairly steadily since 1960. Between 1960 and 2006, estimated production ranged from a low of 1,740 million pounds in 1960 to a high of 11,897 million pounds in 2000. In 2006, eight US manufacturers produced an estimated 11,387 million pounds of styrene; the three largest producers accounted for 54% of production.
US consumption of styrene in 2006 was 9,600 million pounds, > 99% of which was consumed in the production of polymers and copolymers. US imports and exports of styrene increased steadily from 1975 through 2007, from 7 million pounds to 1,475 million pounds for imports and from 574 million pounds to 4,200 million pounds for exports.

The US styrene industry is a diversified approximately $28-billion industry comprising hundreds of companies with thousands of facilities, according to the Styrene Information & Research Center (SIRC). SIRC is a non-profit organization comprising voting member companies involved in the manufacturing or processing of styrene, and associate member companies that fabricate styrene-based products.

On 10 June 2011, the US Department of Health and Human Services (HHS) published the National Toxicology Program’s 12th Report on Carcinogens (RoC) listing styrene as “reasonably anticipated to be a human carcinogen.” Styrene is on the list, HHS said, based on human cancer studies, laboratory animal studies, and mechanistic scientific information.

HHS said that limited evidence of cancer from studies in humans shows lymphohematopoietic cancer and genetic damage in the white blood cells, or lymphocytes, of workers exposed to styrene. Most of the evidence in humans comes from occupational cohort studies in two major industries: (1) the reinforced-plastics industry and (2) the styrene-butadiene rubber industry, according to the RoC.

People may be exposed to styrene by breathing indoor air that has styrene vapors from building materials, tobacco smoke, and other products. The greatest exposure to styrene in the general population is through cigarette smoking. Workers in certain occupations may potentially be exposed to much higher levels of styrene than the general population.

The International Agency for Research on Cancer (IARC) also classifies styrene as a potential human carcinogen.

SIRC contends that styrene’s inclusion is unjustified by the latest science and resulted from a flawed process that focused on only those data that support a cancer concern, and filed a complaint against the listing on 10 June 10, and then on 16 June filed a motion seeking the preliminary injunction.

On 5 July Judge Reggie B. Walton of the US District Court for the District of Columbia denied the SIRC motion. At the conclusion of a 90-minute hearing, the judge asked both parties to establish within two weeks a schedule in which to litigate the merits of SIRC’s claim that styrene should be removed from the RoC. SIRC legal counsel will work with government counsel to develop that schedule while evaluating other possible legal options.

Resources

  • Rebekah McKenna, David R. Nielsen (2011) Styrene biosynthesis from glucose by engineered E. coli, Metabolic Engineering, doi: 10.1016/j.ymben.2011.06.005

Comments

kelly

Nice to know, but what's the relative economics.

fred linn

Just great---the world's oceans and wildlife are choking and dying under a sea of cast off plastic garbage that does not decompose. And to top it all off, it is carcinogenic as well.

And these yahoos are spending time and resources developing ways to make even more of it. Not only that, tinkering with the basic DNA codes that make up the very fabric of all life. What happens if it gets loose in the environment and these e. coli set up shop in your gut happily turning everything you eat into plastic?

This sll sounds so incredibly stupid and sinister I can't even think of anything to say.

The relative economics? Let's all think of ways we can kill ourselves and everything else so we can have lots of cheap plastic junk.

King Midas in reverse.

Jason Marshall

I have to agree with Fred. This is science exploring its worst traits. Again. We appear to need more ethics training in school, and possibly more still post-doc.

It's projects like this that make the anti-GMO people toss and turn at night. This is exactly the trust issue they have with scientists, and why they want the entire discipline to stop: taking pathogenic or pest species and making them do their job BETTER will only teach us a lot if it doesn't kill us all first.

I don't think I have to tell anyone here that e coli gets into humans, and it's infused into our agriculture. You can kill it by cooking, but you can't kill any pathogens it leaves behind.

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