Eat your greens

Scientists are giving plant cells software upgrades to fight climate change

These Frankenstein's monster chloroplasts are designed to efficiently transform CO2 into more useful compounds.

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Carbon emissions are one of the biggest problems facing our world. While emission numbers have seen a modest dip as a result of people hunkering inside during Covid-19, we're going to need a more sustainable solution than keeping people inside indefinitely. And synthetic biologists might just have the answer, thanks to new developments that allow scientists to recreate and control artificial photosynthesis for carbon sequestration.

Using spinach membranes and oil droplets filled with enzymes, a team of European researchers was able to mimic natural plant pathways in an artificial chloroplast and in turn, transform light and CO2 into more useful compounds.

And because the researchers are able to carefully control how photosynthesis takes place, the authors write that in the near future this artificial photosynthesis may be more efficient than its natural counterpart.

"Future implementation of other life characteristics such as self-repair and reproduction, as well as information processing and regulatory circuits, will further contribute to the realization of synthetic organelles and cells from the bottom up that approach—or may even exceed—a grade of organization, integration and functional efficiency comparable to their natural counterparts," write the authors of a new study published Thursday in the journal Science.

"Plant cells or microbial cells are like hardware...With our bottom-up approach, we can actually change the hardware."

Part of what separates this research from the pack is the fact that instead of manipulating existing cell structures, the team was able to use a bottom-up approach to design completely new artificial chloroplasts, coauthor and Director at Max-Planck Institute for Terrestrial Microbiology, Tobias Erb, tells Inverse.

Comparing cells to computers, Erb tells Inverse that by designing their chloroplasts from scratch they're able to upgrade them with much more sophisticated "software" (aka, functionality) than other pre-existing cell structures.

"Usually you take a cell and you modify [it] to integrate a new feature. Here... we put pieces together and built it from scratch," says Erb. "Plant cells or microbial cells are like hardware. What we usually do in biology is we program new functionalities in [cells.] So, you could say that we have software that we put into these cells. With our bottom-up approach, we can actually change the hardware."

While hardware, like an old PC for example, can become too old to run the newest software, Erb says that changing the hardware itself allows them to continue to run more sophisticated "software" in these cells that wouldn't be possible otherwise.

To do this, the team started by extracting membranes from a common salad ingredient: spinach.

By programming these chloroplasts with updated "software," the researchers say they could be even more efficient than the real thing.Science
66,800 acres of spinach were planted in the United States in 2019, according to the USDA.©Daniela White Images/Moment/Getty Images

Thylakoids, little compartments in the spinach plant where photosynthesis takes place, were isolated and encapsulated in small water-in-oil droplets, on the same magnitude of biologic plant cells, Erb tells Inverse. These droplets were then retrofitted with a new pathway for carbon processing called the CETCH pathway.

This pathway, comprised of 16 different enzymes, is meant to mimic six naturally occurring pathways in plants that transform inorganic carbon, like CO2, into useful compounds. Focusing on this single pathway allowed the researchers to optimize the carbon processing reaction, Erb tells Inverse.

Through experimenting with these chloroplasts, the team was able to determine that the chloroplasts were successfully metabolizing light and transforming CO2.

But, that doesn't mean they're ready to roll out into the fight against climate change (or even into new drug synthesis) just yet, Erb tells Inverse.

"At the moment, the objects we've created are just stable for two hours," says Erb. "However, we've demonstrated several times that we can stabilize proteins and enzymes... so this is just an optimization [problem.] I'm pretty sure we can optimize and make these objects much more stable."

As for what these super plant cells will look like, Erb says they're not likely to look like a giant Lion King-esque tree-of-life placed as sentries as coal plants. Instead, they'd likely start by replacing existing cells in industrial manufacturing and optimizing those processes.

"Artificial trees, that's a cool idea," says Erb. "But I would say the first thing we'd see would be in an industrial setup where we already have similar properties with living cells."

Abstract: Nature integrates complex biosynthetic and energy-converting tasks within compartments such as chloroplasts and mitochondria. Chloroplasts convert light into chemical energy, driving carbon dioxide fixation. We used microfluidics to develop a chloroplast mimic by encapsulating and operating photosynthetic membranes in cell-sized droplets. These droplets can be energized by light to power enzymes or enzyme cascades and analyzed for their catalytic properties in multiplex and real time. We demonstrate how these microdroplets can be programmed and controlled by adjusting internal compositions and by using light as an external trigger. We showcase the capability of our platform by integrating the crotonyl–coenzyme A (CoA)/ethylmalonyl-CoA/hydroxybutyryl-CoA (CETCH) cycle, a synthetic network for carbon dioxide conversion, to create an artificial photosynthetic system that interfaces the natural and the synthetic biological worlds.
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