Bacteria produce climate-cooling gas

23 August 2019

COASTLINE-SEAWEED

Mud coastline with seaweed

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We’re all familiar with that strong seaside smell. That is the smell of dimethyl sulfide, or DMS for short, a gas that is produced by many organisms living in and around the sea. That gas may also have a role to play in cooling the climate...

DMS is primarily produced from another compound, dimethylsulfoniopropionate - understandably shortened to DMSP - which also seems to be an all round useful marine molecule. It is food for many sea microorganisms, it helps protect the cells of various marine organisms such as algae from the surrounding salty water, and it may also help these cells to function in low temperature and high pressure environments.

When DMS gets released into the atmosphere, it primarily can act as an aerosol layer to reflect the sun’s rays back up into space, thus having a climate cooling effect, and indirectly, its derivatives help the formation of clouds, which can have the effect of cooling the climate.

Until recently, researchers thought that DMSP and DMS were only created by various forms of seawater plants, such as seaweed, phytoplankton or salt marsh grasses. Now, a new study published in Nature Microbiology seems to suggest that bacteria are also a significant producer of these molecules.

An interdisciplinary team of researchers from China, New Zealand and the UK analysed mud from the salty marshes of the Norfolk coast and from the Mariana Trench in the Pacific Ocean. “Staggeringly, there was about three orders of magnitude higher DMSP concentrations in that surface mud over what you would find in the surface seawater,” explains lead author of the study, Dr. Jonathan Todd from the University of East Anglia, UK.

It turns out that many of the organisms in the mud were bacteria, and around a quarter of the bacteria that the researchers were able to isolate were producing DMSP. The researchers also looked at the genetic profile of the larger community of organisms living in the mud, and found that a large number of the bacteria present there had the genetic potential for producing DMSP. They could then estimate that there are around 100 million bacteria in a gram of mud that can produce DMSP.

“It makes us think that actually, marine sediments in general are pretty important for the production and cycling of DMSP, potentially generating these climate-active gases such as dimethyl sulfide.”

The researchers also investigated mud from the Mariana Trench in the western Pacific Ocean and found that even at depths of over 4km, there were many bacteria producing DMSP and DMS. While the molecules produced at the bottom of the oceans are unlikely to reach the surface and end up in the atmosphere, the production that happens in the coastal sediments does.

Even though DMS is a cooling gas, the researchers emphasised that using it for geoengineering, that is, generating more of it and releasing it into the atmosphere in order to combat climate change, is not really a viable solution at the moment. This is due to the complexity of the global climate and the potential risks and side effects involved. These new findings are however important in developing more accurate models of DMS and DMSP production and cycling, which will in turn inform our understanding of the climate.

“It’s currently perceived that the majority of DMSP and DMS is produced in the surface ocean environment,” says Todd. “What we hope this study does is it challenges this old-held perception, and hopefully makes people believe that bacteria are at least significant producers of these molecules. And indeed that sediments, and these coastal regions, tidal flats, are pretty important to be considered into climate models, which of course, influence policy makers.”

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