Infected plankton: Marine viruses can disrupt the carbon cycle – Wikipedia

RNA viruses don’t just cause infectious diseases like COVID-19 or influenza and rabies. They also play an essential role in the world’s oceans. There, microbes influence the process of photosynthesis, which is the basis of life for most life on Earth, the carbon cycle and thus the climate around the world.

A research team led by Matthew Sullivan, Guillermo Dominguez-Huerta and Ahmed Zayed from Ohio State University deduced this from analyzing the genomes of marine RNA viruses they found in seawater samples. The results of the study have now been published in the journal Science.

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A floating community of living creatures

“This study shows once again how little we know about the oceans,” explains Timo Moritz of the German Maritime Museum in Stralsund, who was not involved in the study. “This applies not only to the deep sea, but also to some extent to very basic processes in surface waters.”

Water samples were collected for analysis during a circumnavigation of the globe with the French research vessel “Tara” in the years 2009 to 2013. On this expedition, the researchers took water samples from depths of up to 1,000 meters at 210 points. From this, they isolated the genomes of many known and thousands of previously unknown RNA viruses. They presented the first results in April in “Science.” In their new publication, US researchers analyze the role these pathogens play in the world’s oceans.

At first glance, viruses should not be a universal player in nature because they cannot reproduce themselves, but they need other organisms to do so. But they are everywhere. According to the new analyzes, RNA viruses in the world’s oceans mainly contain algae and fungi as hosts. Many of these organisms float in water with little or no thrust, and are carried passively by currents. They belong to “plankton”, which derives from the Greek and means “to which one is led.”

Possible malfunction of the carbon pump

Like land plants, algae and other plankton organisms carry out photosynthesis and form biomolecules of carbon dioxide, water and some trace elements. Plankton produce about half of the biomass on Earth. However, RNA viruses interfere with the metabolism of host organisms in order to induce them to produce new viruses. By doing so, they can also reprogram the process of photosynthesis, fundamentally changing the basis of life, Sullivan and his team explain. This in turn affects the climate because algae and higher plants use the greenhouse gas carbon dioxide from the air and water to produce biomass.

If pathogens weaken the algae, vital production falters and takes less carbon dioxide from the air. Plankton form less biomass, from which animals can feed. The climatic balance is also changing: many organisms are decomposed by fungi and microorganisms after their death. Most of the carbon in the air is released back into the air in the form of carbon dioxide which leads to a warming of the climate. However, some organisms sink to the sea floor. So the carbon transported with them disappears from the climate system in the long term.

Sullivan and his team use the frequency of RNA viruses to draw conclusions about this process, known as the “carbon pump.” Therefore, the RNA viruses present in the water have a particularly strong impact on the ecosystem of the polar seas. The team suspects that viruses can stay there longer in the cold and thus improve their chances of finding a host. On the other hand, in warm water, viruses degrade more quickly.

In warm seas such as the coasts of Panama, predators feed on the sea floor (right panel). If their way is blocked, more…Photo: Smithsonian Institution

Predatory fish seem to have a strong influence on the marine communities there. Gail Ashton and Gregory Ruiz of the Smithsonian Environmental Research Center in Tiburon, California, and their team also report it in the journal Science.

The group conducted standardized experiments at 36 sites along the Pacific and Atlantic coasts of North, Central and South America, from which they were able to infer how predators affect the organisms on the bottom. Most of the bottom dwellers disappeared into the warm waters. The team suspects that if climate change continues to warm the world’s oceans, the impact of predatory fish on ecosystems may increase.

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