Tiny ocean plants called diatoms use a single carbon capture pathway

The world's smallest plants, single-cell organisms called diatoms, provide exceptional carbon capture services, according to researchers.

According to a new study, published Monday in the journal Frontiers in Plant Sciences, diatoms mostly use a single cellular pathway to capture and concentrate CO2.

Every year, diatoms floating near the surface of the ocean capture 10 to 20 billion metric tons of CO2 via photosynthesis. Until now, scientists weren't sure how the unicellular plants concentrated CO2 so efficiently.

The latest findings suggest diatoms, sometimes called phytoplankton, use a single pathway to deliver CO2 to a highly efficient carbon fixing enzyme.

"We show that marine diatoms are super smart in fixing atmospheric CO2 even at the present-day level of CO2 -- and the variability in surface seawater CO2 levels did not impact the gene expression and abundance of the five key enzymes used in carbon fixation," lead researcher Haimanti Biswas, principal scientist at CSIR-National Institute of Oceanography in India, said in a news release.

"This answers a key question about how marine diatoms may respond to the future increase in atmospheric CO2 levels," Biswas said.

Though traditional plants use a variety of mechanisms for CO2 capture, they possess only one known carbon-fixing enzyme called RuBisCO, which is thought to be surprisingly inefficient.

To better understand how diatoms concentrate CO2, researchers sequenced the genomes of hundreds of marine plankton samples. Their analysis revealed the abundance and expression of genes responsible for the synthesis of five key enzymes.

Across all the diatom samples, researchers found genes related to one particular enzyme were ten times more abundant.

The importance of the enzyme carbonic anhydrase suggests diatoms are pumping CO2 directly inside their cell walls, instead of first biochemically converting the carbon.

While the abundance of carbonic anhydrase-related gene expression was consistent across all types of diatoms, researches found other gene expression patterns varied in relation to latitude and temperature. Scientists hope to learn more about these patterns in followup studies.

"So far, our study indicates that despite variability in CO2 levels, these tiny autotrophs are highly efficient in concentrating CO2 inside the cell," said Biswas. "That's the probable reason for their ability to fix nearly one-fifth of the global carbon fixation on earth."

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