Science. Les viruses marins, une “matière noire” qui affecte le climat

The ocean is dominated by communities of plankton (1) that are essential to the maintenance of life on Earth. By producing energy and organic matter through photosynthesis, they generate as much oxygen and absorb as much carbon dioxide as trees. The plankton is also at the base of the maritime alimentary chain and therefore indirectly terrestrial.

Au cœur de la pompe à carbone biologique

Its impact is essential because it pilots the biogeochemical cycles of our planet, that is, the processes of transport and transformation of a chemical element (for example, carbon) between the great reservoirs of our planet. la terre (géosphère), l’air (atmosphère) et les océans (hydrosphère).

The plankton appears therefore au cœur de la pumpe à carbone biologique. Its activity determines whether the dissolved carbon dioxide is assimilated to the biomass (sequestered in the depths when the plankton dies), recycled in the surface water or released into the atmosphere. Or, ce plankton est sensitive aux viral infections…

LA MORT MASSIVE DE CELLULES AGRÈGE UNE “NEIGE” COMPOSÉE DE CARBONE, QUI VA TOMBER au fond de l’océan. Chris Bowler, biologist

In the world of marine microbiology, DNA viruses are more and more known. They influence marine micro-organisms and therefore their associated biogeochemical cycles. But other marine viruses, with RNA this time (the Sars-CoV-2 is, for example, an RNA virus) are less well known because they are still abundant in the ocean.

A living cell rests on the surface

“Nous ne savons pas grand-chose sur ces virus que nous appelons “matière noire” de l’océan. Their diversity and their role in marine ecosystems are une grande inconnue,” explains Chris Bowler, head of the laboratory of genomics of algae and plants at the École normale supérieure de Paris. With colleagues from around the world, he participated in a study published recently in the review “Science” (2), which aimed to characterize the first marine RNA viruses.

Pour cela, les chercheurs ont utilisate des prélèvements réalisés par l’expédition Tara Océan between 2009 et 2013. Pourquoi dix ans après ? “Characterizing les viruses à ARN est beaucoup more complexe que characteriser ceux à ADN. These are our colleagues in the United States who have developed methods to do this. Chris Bowler continues. Si bien que, dans leur publication, 5 500 viruses à ARN différences sont characterized. In infecting photosynthetic organisms, viruses impact the carbon cycle.
It is through this cycle that the transfer of carbon will be done from the atmosphere to the bottom of the oceans. Une cellule vivante reste en surface. Quand “le virus tue la cellule hôte, elle explose et le carbone capté lors de la photosynthèse est relâché dans l’environnement. This massive death of cells can cause an aggregation of organic matter, composed of carbon, and generate the so-called “marine snow” that will fall to the bottom of the ocean, “says the researcher.

C’est entre autres comme cela que les viruses à ARN jouent sur le cycle du carbone et donc sur le changement climatique. Mais c’est une donnée encore trop peu connue que la publication vient completer. These characterizations provide a roadmap for the study of RNA viruses in nature and their role in the evolution of life on Earth (read “point of view” below).

(1) The term plankton designates the ensemble of organisms that allow themselves to be driven by currents.
(2) “Diversity and ecological footprint of global ocean RNA viruses”, “Science”, 2022.


The point of view

“Marins’ ARN viruses are new to science”

Chris Bowler, biologist, directeur de recherche au CNRS et à l’ENS, Chef du laboratoire génomique des algues et des plants.

Comment se comportent ces virus à ARN?

They are close to DNA viruses. Seul le patrimoine genetic change. In termes d’infectiosité, le cycle est très similaire. They are not more “evil” than DNA viruses. Chez l’homme, le VIH, la grippe ou le Sars-CoV-2 are viruses à RNA. Ils “aient” les humains. Il n’y a pas de distinction, pas de partialité dans les interactions avec les hôtes.

There is a direct link between the virus and CO2:?

No, the lien is indirect en positive or negative. By infecting organisms involved in photosynthesis, killing cells and causing “marine snow”, carbon can be transported to the ocean floor.

If the infected organism is large, the contribution to the transport of carbon towards the bottom of the ocean will be potentially more important because the organisms are heavier and will cool. Thus, diatoms (microalgae) are 1,000 times larger than bacteria. So a virus that infects a bacteria or a diatom will have very different impacts because the amount of carbon released is different.

But, de la même façon, en tuant les cellules, il y en a moins pour la photosynthèse et donc le carbone est moins absorbedé, c’est l’aspect négative. Even if viruses do not do photosynthesis, even if viruses are not alive, they have the possibility to impact the carbon cycle and therefore climate change.

Tous les organisms ne sont pas infectedes de manière identique?

Nous manquons de modèles hôtes/pathogenes pour étudier les infections en laboratory. Nous avons décrit 5,500 types of virus ARN, but we don’t know who infects who? Algues, zooplankton, poissons? Il nous reste à mettre au point les techniques pour mieux comprendre ces interactions. One could cultivate the diatoms, find the viruses that infect them, characterize them and better know the processes.

Par ailleurs, la grande majority des viruses à RNA marines sont nouveaux pour la science. They probably represent very ancient lineages, they are different from the “classic” RNA viruses that we know. On voit toute l’évolution de la vie sur Terre à travers l’étude de ces viruses.

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