Manufacturing Enzymes to Save World from Climate Change

Trying to stop climate change is a tough challenge to overcome. With carbon dioxide levels running amok since the Industrial Revolution almost two centuries ago, it’ll be difficult to undo that damage in a shorter amount of time. Luckily, humanity has been gifted with intelligence and adaptability where our scientists seek to solve these problems — artificial or otherwise. One such solution is a rather new one: finding enzymes that’ll speed up the photosynthetic process in plants beyond their natural means.

As reported by Motherboard last month, scientists from both the Department of Energy’s Joint Genome Institute and Germany’s Max Planck Institute for Microbiology in Marburg have come up with enzymes meant to catalyze natural photosynthesis in plants. In other words, they’ve found a way to make plants convert carbon dioxide into oxygen more efficiently.

“We had seen how efforts to directly assemble synthetic pathways for CO2-fixation in a living organism did not succeed so far,” said Tobias Erb from the Max Planck Institute in a statement detailing the enzyme project. “So we took a radically different, reductionist approach by assembling synthetic principle components in a bottom-up fashion in a test tube.”

Instead of focusing on chemistry, Erb and his team have been studying biology and implementing, as he calls it, synthetic biology. The natural enzyme, known as RuBisCO, is responsible for plants fixing carbon dioxide and breaking it down into oxygen and water vapor. While it gets the job done, it does so slowly at around 5 – 10 CO2 molecules a second. The enzyme synthesized in the lab (Enoyl-CoA carboxylase/reductase or ECR for short), by comparison, fixes 80 CO2 molecules a second, an 8- to 16-fold increase.

In order to develop these enzymes, the scientists use a process called metabolic retrosynthesis where they draw out metabolic pathways on paper in order to find which enzymes they can utilize the best. “You need to look into biology, you need to look into microorganisms… you need to look into plants. You need to find all the individual enzymes that could do the job.”

So far, they’ve isolated about 17 different enzymes from nine different organisms, three of which having been redesigned synthetically to better suit the team’s purposes. The goal is to get these enzymes to all work in tandem rather than separately so they can work as efficiently as possible.

After finding the enzymes, the goal is to then demonstrate a cycle in which they can fix carbon effectively, proving the scientific theory works. While they’ve yet to apply the enzymes to living organisms, the team has successfully gotten their new cycle to work.

“At the moment, the cycle is proof of principle,” Erb continues. “It’s an in vitro cycle that can fix CO2. The big question is where do we want to go with this?”

One suggestion is to skip plants altogether and apply the enzymes to artificial organelles and leaves: a completely synthetic plant that does the job of photosynthesis 20 times more efficient than natural plants.

Another suggestion is to transplant the cycle into natural plants such as algae, giving them their own boost and successfully breeding this trait to promote highly photosynthetic flora. Since plants have played a major role in keeping our ecosystem balanced, it makes sense to help tip the balance away from the carbon heaviness of the post-Industrial Revolution world in favor of oxygen-producing plant life. Though this isn’t the only way we’ve tapped into carbon sequestration and photosynthesis.

The Art of Carbon Fixation

The joint enzyme research done by the Department of Energy and Max Planck Institute is just the first step in adding synthetic biology to the growing list of ways to harness atmospheric carbon dioxide. As the DoE’s DNA Synthesis Science group’s head Yasuo Yoshikuni mentioned, “In the longer term, we hope to expect to see these test-tube results yield a new generation of real bioproducts delivered to address critical energy and environmental challenges.” Aside from artificial leafs and boosting natural flora, carbon-based cattle feed and rethinking and designing different chemical products based on this new enzyme cycle are also possible approaches using ECR.

One thing that would be interesting to see is how these efficient-enzyme plants react to the treatment and if it does, indeed, rebalance atmospheric gases to healthier levels. Though not to spark concern, it does raise the question of what if the process is too efficient and then shifts the balance to too much oxygen production? But that’s a whole other problem that ought to be faced if we even get close to that bridge. For those who are interested in learning more, however, the teams have already published their findings in Science Magazine for your perusal.

Still, other less biological methods have been tested and applied in order to tackle our current problem of rapidly-rising carbon dioxide levels. A geothermal power plant in Iceland, for example, sequests its carbon dioxide into stone. Using a revolutionary process aptly named CarbFix, carbon dioxide along with hydrogen sulfide are injected as a slurry into basalt where, after “incubating” in rods, the molecules mineralize to covert the rock into limestone.

For those worried about the carbon dioxide then leaking from this rock, you needn’t be too concerned. Chemically, the CO2 reacts with the calcium oxide (CaO) and magnesium oxide (MgO) of the basalt to form the limestone itself, otherwise known as calcium carbonate (or CaCO3). In other words, there’s no carbon dioxide to leak since it’s no longer truly carbon dioxide at all.

Closer to home, the University of Illinois at Chicago has taken on both sides of the carbon problem, potentially reducing emissions as well as scrubbing the atmosphere of existing gases. Earlier this summer, they managed to develop a photocell that uses manmade photosynthesis to produce tangible fuel (also known as Syngas). Able to be burned as a fuel on its own or converted to other contemporary hydrocarbon fuels such as diesel, this photocell — once scaled for industrial application — starts out competitively with current fossil fuel refining. Given that, further advancements and investments with this technology will effectively see it as an even cheaper method to refine fuel than gasoline and oil.

What’s more, even if standard combustion engines are still used to power vehicles, the photocell just scrubs any emited carbon dioxide and recycles it back into fuel, effectively nullifying output.

Certainly, global warming due to carbon dioxide emission is a problem we’ve just begun to really make meaningful strides to solving. And while the news may seem grim as ice caps slowly melt and our oceans and atmosphere warm up, it’s heartening and inspiring to know that there are plenty of people working diligently to solve these problems. You don’t need to be an ultra smart scientist to make meaningful environmental change either, but as long as you have your heart in the right place, our Earth still has a fighting chance.