Tiny Ocean Organisms Play a Surprisingly Big Role in Regulating the Climate

May 17, 2016 | Joanne Kennell

Water surface
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They are the most abundant organisms on Earth.

The world’s oceans are crucial for heating the planet and regulating its climate. The majority of the sun’s radiation is absorbed by the oceans, which act like massive heat-retaining solar panels, and Earth’s atmosphere also plays a role by retaining heat that would otherwise radiate back into space after sunset.

But the ocean doesn’t just store solar radiation, it also helps redistribute heat around the globe. Now, scientists have discovered that a tiny ocean organism plays a more important role in the regulation of Earth’s climate than previously thought.

The bacteria group Pelagibacterales are believed to be the most abundant organisms on Earth, comprising up to half-a-million bacterial cells in every teaspoon of sea water. And according to new research published in the journal Nature Microbiology, they also stabilize Earth’s atmosphere.

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For the first time, an international team of researchers have identified Pelgibacterales as a likely source for the production of dimethylsulfide (DMS), which is known to stimulate cloud formation, and is also a key component in the CLAW hypothesis.

Under the CLAW hypothesis, the temperature of Earth’s atmosphere is stabilized through a negative feedback loop where sunlight increases the amount of certain phytoplanktons, which in turn produce dimethylsulfoniopropionate (DMSP). DMSP is broken down into DMS by Pelagibacterales. Then, through a series of chemical processes, DMS results in an increase of cloud droplets, which in turn reduces the amount of sunlight hitting the ocean surface.

"What's fascinating is the elegance and simplicity of DMS production in the Pelagibacterales. These organisms don't have the genetic regulatory mechanisms found in most bacteria,” Ben Temperton, lecturer in the department of Biological Sciences at the University of East Anglia (UEA) and a member of the international team of researchers, explained in a UEA press release.

“Having evolved in nutrient-limited oceans, they have some of the smallest genomes of all free-living organisms, because small genomes take fewer resources to replicate,” Temperton continued.

Since Pelagibacterales were found to generate DMS by a previously unknown enzyme, which is also present in many other marine bacterial species, scientists may have been underestimating the microbial contribution to the production of DMS.

Pelagibacterales are likely an important component in the climate’s stability, so to improve models of how DMS impacts Earth’s climate, researchers need to start considering this tiny organism as a major contributor.

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