A pair of rare enzymes in marine microorganisms could boost carbon storage

Researchers at Stanford University have discovered a surprising genetic twist in the lineage of microorganisms that may play an important role in storing ocean carbon. This microorganism, known as blue-green algae or cyanobacteria, has two different forms of the ubiquitous enzyme that are rarely present at the same time in the same organism.

“This is a great example of science where you go out looking for one thing and end up finding something else that’s even better,” said Anne Dekas, an assistant professor of Earth system science at the Stanford Doerr School of Sustainability. That’s one example.” Senior author of the study published in the Proceedings of the National Academy of Sciences.

Billions of years ago, long before plants appeared, cyanobacteria invented oxygenic photosynthesis. In the process of producing food from carbon dioxide and sunlight, a wide range of microorganisms released oxygen into the air, making Earth’s atmosphere hospitable to the variety of life on Earth today.

“Cyanobacteria are probably the most important life forms on Earth,” Dekas says. “They supplied oxygen to Earth’s atmosphere and sparked a biological revolution.”

special cyanobacteria

Similar to plants, cyanobacteria use an enzyme called ribulose diphosphate carboxylase, or Rubisco, to convert carbon dioxide into biomass. Rubisco, one of nature’s most abundant proteins, comes in several forms. The most common type, known as type I Rubisco, often uses structures called carboxysomes to selectively react with carbon dioxide rather than oxygen, allowing photosynthesis to proceed efficiently. Organisms with a less common type of enzyme, known as type II, lack carboxysomes and can effectively build biomass from carbon dioxide even in oxygen-starved environments.

Lead author Alex Jaffe, a postdoctoral fellow in Earth system science, said that living organisms typically have only one form of Rubisco. So he was surprised when he came across an exception to that rule while studying carbon fixation in marine microorganisms. Jaffe was analyzing DNA in seawater samples taken from the deep sea off the coast of Central and South America when he noticed that shallow-sea DNA samples had been accidentally mixed in. He found that the cyanobacteria in these samples appeared to carry both Rubisco-type genes.

“My first reaction was that this was probably wrong,” Jaffe said.

Further research confirmed that both forms of the enzyme are present and actively used in photosynthesis by shallow-sea cyanobacteria, but understanding how cyanobacteria utilize these two forms remains unclear. additional testing is required.

“Having two versions could potentially remove more carbon dioxide from the water or remove it a little more efficiently than if you only had one,” Jaffe said.

Where the samples were taken, an oxygen minimum zone about 50 to 150 meters below the surface where both oxygen and light are scarce, efficiency may be the key to survival.

“It’s very difficult to live there,” Decas said. “For photosynthetic organisms, low light means little energy.”

Carbon storage and super efficient crops

The discovery could help scientists predict how the ocean’s ability to sequester carbon will change as hypoxic zones expand due to climate change. The discovery that some cyanobacteria have both forms of Rubisco suggests that cyanobacteria store carbon more efficiently than previously understood and may thrive as the oxygen minimum zone expands. suggests.

If indeed two Rubiscos are better than one, this discovery could also lead to more efficient crop production. For decades, researchers have been trying to engineer Rubisco type I to grow more crops with less fertilizer and water.

“We’re looking forward to continuing to think about this with the people who work on the plant engineering side to see if we can get some results, both literally and figuratively,” Jaffe said. spoke.

This discovery gave Jaffe a new understanding of life’s ability to adapt to difficult environments. “Despite being central to an organism’s metabolism, these genes are actually very flexible and can be reorganized and shuffled around in ways we don’t expect,” he said. Said.