Thousands of mysterious viruses that have recently been discovered in the world’s oceans could exert enormous influence on ecosystems, in part by “reprogramming” the hosts they infect, scientists have reported.
The new research, published Thursday, June 9 in the journal Science (opens in a new tab)focuses on viruses that contain RNA, a molecular cousin of DNA. Examples of RNA viruses abound in human disease; for example, coronavirus and flu viruses are both RNA-based. However, when it comes to RNA viruses in the ocean, scientists are just discovering the variety that can be found and the range of hosts that they can infect.
Based on the new study, “we are sure that most RNA viruses in the ocean infect microbial eukaryotes, so fungi and protistsand to a lesser extent, invertebrates,” co-first author Guillermo Dominguez-Huerta, who was a postdoctoral researcher in viral ecology at Ohio State University (OSU) at the time of the study, told Live Science. eukaryotes are organisms with complex cells that contain their genetic material inside a nucleus.
These viral hosts, namely fungi and protists, which include algae and amoebas – pull carbon carbon dioxide out of the atmosphere and therefore influence the amount of carbon that ends up being stored in the ocean. By infecting these organisms, the RNA virus likely affect how carbon circulates in the ocean as a whole, said Steven Wilhelm, principal investigator of the Aquatic Microbial Ecology Research Group at the University of Tennessee at Knoxville, who was not involved in the study. new study.
Related: 70,000 never-before-seen viruses found in human gut
“Given the abundance of RNA virus particles, the knowledge that they can do so continues to build the story of how important viruses are in the world when it comes to the flow of energy and carbon.” , Wilhelm told Live Science in an email.
(Wilhelm collaborated with several of the study’s authors, including Matthew Sullivan and Alexander Culley, on projects unrelated to the new study.)
Viruses, viruses everywhere
Earlier this year, Dominguez-Huerta and colleagues reported finding more than 5,500 previously unidentified RNA viruses in the world’s oceans.
For this study, published on April 7 in the journal Science (opens in a new tab)the team analyzed 35,000 water samples that had been collected from 121 sites across five oceans by the Tara Oceans Consortium, an ongoing global study examining the impact of climate change on the oceans. These water samples were teeming with plankton – tiny organisms that drift in the current and often serve as hosts for RNA viruses. To spot the viruses in these planktons, the researchers sifted through all the RNA in the plankton cells to find a specific snippet of genetic code, called the RdRp gene.
“It’s the only… coding sequence common to all RNA viruses,” said Dominguez-Huerta, who currently works as a scientific consultant with a company called Virosphaera; however, the RdRp gene is absent from cells and other virus types.
Ultimately, the team found so many RNA viruses lurking in plankton that they proposed doubling the number of RNA virus phyla – the broad taxonomic category just below “kingdom” – from five to 10 to rank them all.
From there, the researchers wanted to better understand how these viruses are distributed across the world and which hosts they target.
Scientists have determined that viral communities can be categorized into four broad areas: Arctic, Antarctica, Temperate and tropical epipelagic, i.e. near the surface of the ocean, and Temperate and tropical mesopelagic, i.e. between 656 and 3,280 feet (200 to 1,000 meters) under water. Interestingly, virus variety seemed highest in polar areas, although there was a greater variety of hosts to infect in warmer waters.
Related: Under the sea: 50 breathtaking images of our oceans
“Viruses, when it comes to diversity, didn’t really care about cold water temperature,” said co-first author Ahmed Zayed, a researcher in OSU’s Department of Microbiology. This finding suggests that, near the poles, many viruses are likely competing for the same hosts, Zayed told Live Science.
To identify these viral hosts, the team used several strategies; for example, one method involved comparing the genomes of RNA viruses with known hosts to those of newly discovered viruses, and another involved searching for rare snippets of viral RNA in the genomes of host cells, where bits of RNA can sometimes be left behind. This analysis revealed that many RNA viruses in the ocean infect fungi and protists, some infect invertebrates, and a tiny fraction infects bacteria.
The team also unexpectedly found that 95 of the viruses carried genes they had “stolen” from their host cells, Dominguez-Huerta said. In the host, these genes help direct metabolic processes within the cell. This finding suggests that the viruses have disrupted the metabolism of their hosts in some way, likely in order to maximize the production of new virus particles, the authors concluded.
Some smaller-scale studies had hinted at this gene-scanning ability in the past, Dominguez-Huerta noted.
After identifying hosts susceptible to infection by the ocean viruses, the team determined that around 1,200 of the viruses may be involved in carbon export – the process by which carbon is removed from the atmosphere, incorporated into marine organisms and then “exported” to the depths of the sea. because these organisms sink to the bottom of the sea after they die.
The deeper these carbon stores sink, the longer they are likely to remain stored in the ocean before being released back into the atmosphere, according to the Monterey Bay Aquarium Research Institute (opens in a new tab). For this reason, carbon export is an important factor that scientists incorporate into climate change models. The new study suggests that infection of marine organisms with RNA viruses may be another, previously unrecognized factor driving carbon flux in the oceans, as viruses alter the cellular activity of hosts they infect.
RNA viruses can also drive carbon flux by opening up their hosts and dumping sequestered carbon into the ocean, Wilhelm said, because viruses often burst from their hosts after rapidly replicating inside.
Originally posted on Live Science.