Thousands of mysterious viruses recently lurking in the world’s oceans could have a huge impact on ecosystems, in part by “reprogramming” the hosts that infect them, scientists reported.
The new research, published Thursday (June 9) in the journal Science (opens in new tab)targets viruses that RNA, a molecular cousin of DNA. Examples of RNA viruses abound in human diseases; for example, coronaviruses and influenza viruses are both RNA based. However, when it comes to the RNA viruses in the ocean, scientists are just learning about the variety that can be found and the range of hosts that can infect them.
Based on the new study, “we are confident 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 keep their genetic material in a nucleus.
These viral hosts – namely fungi and protists, including algae and amoebae – Pull carbon CO2 from the atmosphere and thus affect the amount of carbon stored in the ocean. By infecting these organisms, RNA viruses likely affect how carbon flows through the ocean in general, said Steven Wilhelm, the principal investigator of the Aquatic Microbial Ecology Research Group at the University of Tennessee Knoxville, who was not involved in the new study.
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“Given the abundance of RNA virus particles, the knowledge that they can do this continues to build the story of how important viruses are in the world in regards to how energy and carbon flow,” Wilhelm told Live Science in an email.
(Wilhelm has collaborated with several study authors, including Matthew Sullivan and Alexander Culley, on projects unrelated to the new study.)
Virus, virus everywhere
Earlier this year, Dominguez-Huerta and his colleagues reported finding over 5,500 previously unidentified RNA viruses in the world’s seas.
For that study, published April 7 in the journal, Science (opens in new tab)the team analyzed 35,000 water samples collected from 121 sites across the five oceans by the Tara Oceans Consortium, an ongoing global study of the impact of climate change on oceans. These water samples teemed with plankton — tiny organisms that float in the current and often serve as hosts for RNA viruses. To discover the viruses in this plankton, the researchers searched all the RNA in the plankton’s cells to find a specific piece of genetic code called the RdRp gene.
“That’s the one…coding sequence common to all RNA viruses,” said Dominguez-Huerta, who currently works as a scientific consultant at a company called Virosphaera; however, the RdRp gene is absent in cells and other types of viruses.
Ultimately, the team found so many RNA viruses tucked away in the plankton that they proposed doubling the number of RNA virus phyla — the broad taxonomic category just below “kingdom” — from five to ten to classify them all.
From there, the researchers wanted to better understand how these viruses are spread around the world and which hosts they target.
The scientists determined that the viral communities could be divided into four major zones: the ArcticAntarctic, temperate, and tropical epipelagic, meaning close to the ocean surface, and temperate and tropical mesopelagic, meaning about 656 to 3,280 feet (200 to 1,000 meters) underwater. Interestingly, the variety of viruses seemed to be greatest in the polar regions, despite there being a greater variety of hosts to infect in warmer waters.
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“Viruses, when it comes to diversity, didn’t really care how cold the water is,” said co-first author Ahmed Zayed, a research scientist 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 the newly discovered viruses, and another involved hunting for rare fragments of viral RNA in the genome of host cells, where fragments of RNA sometimes remain. This analysis revealed that many of the RNA viruses in the ocean infect fungi and protists, infect some invertebrates and a tiny fraction. bacteria†
The team also unexpectedly found that 95 of the viruses carried genes they “stole” from their host cells, Dominguez-Huerta said. In the host, these genes help to direct metabolic processes in the cell. This discovery suggests that the viruses somehow tampered with their hosts’ metabolisms, likely to maximize production of new virus particles, the authors concluded.
Some smaller-scale research had suggested this gene-sweeping ability in the past, Dominguez-Huerta noted.
After determining which hosts are likely to infect the ocean viruses, the team determined that about 1,200 of the viruses may be involved in carbon export — the process by which carbon is taken from the atmosphere, taken up into marine organisms, and then “exported” to the deep sea if those organisms sink to the seabed after death.
The deeper these carbon stocks sink, the longer they are likely to remain in the ocean before being cycled back into the atmosphere. according to the Monterey Bay Aquarium Research Institute (opens in new tab)† For this reason, carbon exports are an important factor that scientists include in climate change models. The new study suggests that the infection of marine organisms by RNA viruses may be another previously unrecognized factor driving the flow of carbon in the oceans, in that the viruses alter the cellular activity of the hosts they infect.
RNA viruses can also stimulate carbon flow by splitting open their hosts and spilling sequestered carbon into the ocean, Wilhelm said, because viruses often burst out of their hosts after quickly replicating in them.
Originally published on Live Science.