Drop by Drop

Understanding cells’ liquid compartments could help mop up carbon

Portrait photo of young bearded man sitting in armchair in front of a window
FILE—Bajaj in Jan. 2020. Image: Stephanie Dutchen

Lakshya Bajaj had just moved from Houston to become a postdoctoral researcher in the lab of geneticist Scott Kennedy at Harvard Medical School. On a call with his father back home in India, Bajaj tried to convey his excitement about studying how worm cells use liquid droplets to perform critical tasks such as suppressing unwanted gene activity.

Skeptical about the work, his father asked: “Why don’t you do something important, like about the climate?”

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Bajaj knew his research had plenty of importance for uncovering biological principles that could illuminate human health and disease. Still, the comment got him thinking.

India has suffered more heat waves, floods, and droughts as the planet warms, driving up poverty, illness, and death. Even before the COVID-19 pandemic hit, Bajaj and his wife decided against taking their newborn son to Delhi because the winter smog had grown thick enough to block the sun.

Could his work with worms be of any help?

“We’re at Harvard,” Bajaj thought. “We’re the people who can make a difference.”

Serendipity struck when the HMS Genetics Department launched a competition inviting trainees to adapt their research to address climate change. Bajaj had a brain wave.

Scientists aiming to remove extra carbon dioxide from the atmosphere have looked to cyanobacteria. These ocean-dwelling microorganisms contain cell compartments called carboxysomes that are considered “the most efficient carbon-fixing machines on Earth,” said Bajaj.

The enzyme-loaded carboxysomes suck in carbon dioxide and break it down into oxygen and carbon needed for growth and other life-sustaining processes.

Scientists have tried to genetically engineer plants to produce carboxysomes so the plants can siphon more carbon dioxide from the air, but so far, such attempts have failed. Bajaj believes that’s in part because too much remains unknown about the basics of carboxysome structure and function.

“We need to understand carboxysomes before we start trying to put them into crops,” he said.

That’s where Bajaj saw an opportunity to contribute.

P granules
P granules, tagged in green, exhibit liquid-like behavior in worm cells. Animation: Lakshya Bajaj

Most compartments in plant and animal cells are enclosed by membranes that keep their contents separate from the cytoplasm. Some, however, float around in membrane-free droplets that remain as self-contained as oil in water. Worms use the contents of these liquid compartments to control RNA quality, guide embryonic development, and respond to stress.

Bajaj was already developing a protocol to isolate and study the worms’ liquid cell compartments. Why not adapt the protocol to study carboxysomes and find out whether they, too, exist as liquid droplets?

His proposal was named a finalist in the competition, netting $100,000.

Bajaj has been putting the funds to use. He’s perfecting his protocol in worms. He’s working with competition winner Max Schubert to grow healthy batches of cyanobacteria and create a Boston-wide community interested in cyanobacteria research. Soon, he’ll look for signs of liquid phase separation around carboxysomes in the microorganisms.

He hopes the work will one day contribute to mitigating climate change by illuminating “what carboxysomes are doing” and revealing ways to either safely introduce them into plants or make cyanobacteria themselves more efficient at sequestering carbon.

For Bajaj, the project offers a way to connect with both the older and younger generations of his family. He’s working on something his parents agree is important, and he takes comfort in knowing that even if this endeavor doesn’t bear fruit, he can tell his son one day that he tried his best.

“You want to tell your kids, when everything went down with climate change, we were on the right side, trying to fix it,” he said.