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Synthetic biology pulls carbon dioxide out of the atmosphere

A suite of enzymes borrowed from humans, plants, and other life-forms can turn the greenhouse gas into industrial building block chemicals

by Sarah Everts
November 17, 2016 | APPEARED IN VOLUME 94, ISSUE 46

Credit: C&EN/Shutterstock
With every round of the synthetic CETCH cycle, two carbon dioxide molecules are pulled out of the atmosphere. One of those CO2-fixing reactions, in which the enzyme CCR (crotonyl-CoA carboxylase/reductase) attaches CO2 to the organic molecule crotonyl-CoA, is shown here.

Although plants have been turning atmospheric carbon dioxide into useful carbon compounds for millions of years, the enzyme used to do this transformation, called rubisco, is both slow and fickle—it fixes oxygen instead of CO2 about 20% of the time.

So a team of researchers led by Tobias J. Erb at the Max Planck Institute for Terrestrial Microbiology decided to make a synthetic biology system that fixes CO2 more efficiently than plants.

They started with a CO2-fixing enzyme from the pink proteo­bacterium named Methylobacterium extorquens. The enzyme, called crotonyl-CoA carboxylase/reductase, is about 20 times as fast at fixing CO2 as rubisco in plants.

Next the researchers selected a motley crew of 16 additional enzymes from nine other life-forms—including humans, plants, and microorganisms—to run the world’s first CO2-fixing cycle in a test tube (Science 2016, DOI: 10.1126/science.aah5237).

The final output of the newly crafted cycle, named CETCH, is the two-carbon glyoxylate, which could then be converted to industrial products, such as biofuels or pharmaceuticals.

Increasing CO2 concentration in the atmosphere is a problem, Erb says. “But at the same time, it is also a carbon source from which we can make useful compounds.”

The energy-efficient CO2-fixing pathway is a breakthrough for synthetic biology, and it extends “the capabilities for recapturing atmospheric CO2 for use as a carbon feedstock,” say Fuyu Gong and Yin Li at the Chinese Academy of Sciences in a commentary on the new study (Science 2016, DOI: 10.1126/science.aal1559). However, the next step—transplanting the system into an organism and getting the various enzymes to function optimally—will be a huge challenge, they add.



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Michael Deangelo (November 17, 2016 11:56 PM)
Many will probably not agree with my statement, but one should at least give it some thought, if not some merit..

Science / Hypothetical comment:

Using the Human body and (toxins) as my example to lead into this topic, I think it will show a good example of my point -

When people smoke cigarettes, there are toxins taken in and in response, the body response releasing "cleansers and enzymes" are released and over time a balance is reached -

In 2004, the University of Pittsburgh did a study over 5 years of smokers who quit that had smoked for 20 years or more. What they found was alarming - 42% who quit developed cancer (anyway) and not always lung cancer. -

What they learned as that the enzymes that were released while the person smoked, keep the balance of cleansing the lungs, however after they quit, this enzyme continued to be produced and now believed is the cause of some cancers -

Using these "thoughts" for this topic, pulling Co2 out of the air sounds like a good idea but could also be upsetting a balance which has formed over time...Without knowing what is or isn't a "good balance" - to begin with because we don't have this status, what might the impact be?

Co2 is used of course by plant life as well, needed for other forms of life - If we pull to much out of the air, then what? What impact might this have which nature developed over time to keep balance, now it becomes upset...

I think this should be weighed carefully before people assume that having LESS Co2 in the air is actually really better -

Political Social comment:

Personally, Global Warming to me is nothing but a hoax, its a way to pull tax dollars and control lives of people. I can already see "Carbon Credits" being afforded to homes and apartment buildings to be given an "ALLOWANCE" of Carbon credits per person and or per family....Then if that family grows adding a dog or new child, well - that's more "exhaling" and thus, more carbon which of course now means more carbon tax......

Don't doubt me - We have very sick people out there which I just gave them an idea - You'll be paying "fines" or CARBON TAXES because your apartment was allocated to have 20lbs per carbon per 1000 sq feet - and if you exhale too much? - Well, the Govt. will be there with a bill...Have a kid? Expect to pay more.....Add a dog? well, you get the point....
Tariq Bhatti (November 18, 2016 7:29 PM)
Such specious arguments are a cynical attempt to muddy the water on an important issue. It is not an honest attempt at scientific discussion. With such anti-intellectualism becoming rife, more than ever it's important to call out fools when we see them. Let me refer you to an article from this very magazine from last year:

If the entire chemical industry used CO2 as a feedstock for all of its products, only 300 million metric tons of CO2 would be consumed. Compare this the 35 billion metric tons of anthropogenic CO2 released into the atmosphere in 2014 alone. In light of this, the suggestion that new carbon fixation technologies may be to the detriment of plant life or to the atmosphere are insane. It's a willful misdirection of attention from the dire problem that *is* affecting the habitability of this planet: the uncontrolled, anthropogenic CO2 emissions that are overwhelming the planet's feedback loops. We're unlikely to ever fix more carbon than we emit; the best (and really, the far out, rosy-pictured, ultra-optimistic best) we could hope to do is break even--to fix as much carbon as we emit.

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