How RNA viruses are secretly ruling the oceans

Thousands of RNA viruses recently identified in the world’s oceans could have an enormous impact on ecosystems. By reprogramming the hosts they infect, they could actually have an unprecedented impact on the carbon cycle.

marine viruses

An RNA virus is a virus whose genetic material consists of RNA, a molecular cousin of DNA. Many examples of these pathogens are known on land, some of which are known to infect humans. Corona viruses and influenza viruses are examples. On the other hand, those that develop in the oceanic environment are still very little known. How many are they ? Which hosts do they infect?

Earlier this year, a team of researchers led by Ohio State University’s Guillermo Dominguez-Huerta reported finding more than 5,500 previously unidentified RNA viruses in the world’s oceans. For this work, which was published in the journal Science in early April, the researchers analyzed 35,000 samples from collected water 121 locations in the five oceans of the world. These water samples were teeming with plankton, small organisms at the bottom of the food chain. The latter also often serve as hosts for RNA viruses.

To identify the presence of the pathogens, the team scoured the total RNA in the plankton cells to find a specific snippet of genetic code called the RdRp gene. It is a coding sequence common to all RNA viruses. Eventually, the researchers had identified so many new RNA viruses that they proposed it twice as many known phyla (major taxonomic categories) to be able to classify them all.

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A role in the carbon cycle

Since then, researchers have been trying to better understand how these viruses spread across the marine world, but also the hosts they infect. In a new study published in the journal Science, they found that viral communities can be categorized four main areas : Arctic, Antarctic, temperate and tropical epipelagic zone (near the surface) and temperate and tropical esopelagic zone (between 200 and 1,000 meters). Interesting point: the variety of viruses seemed higher in polar regionsalthough in warmer waters there is a greater variety of hosts that can become infected.

To identify these hosts, the team employed several advanced strategies. These analyzes eventually revealed that many RNA viruses infect in the ocean fungi and protists. Some also infect invertebrates, while a very small proportion infect bacteria.

However, fungi and protists, which include algae and amoebas, are known Extract carbon dioxide from the atmosphere. Therefore, through their actions, these organisms affect the amount of carbon that is ultimately stored in the ocean.

In fact, the team unexpectedly discovered that many of these viruses carried genes that were ‘stolen’ from their host cells, thus interfering with their metabolism in one way or another, likely to maximize the production of new virus particles. Thus, by infecting these hosts, RNA viruses would also affect the circulation of carbon in the ocean. This new study thus suggests that RNA virus infection of marine organisms may be a previously unrecognized factor that should finally be included in climate models.

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