Scientists discover viruses that secretly rule the world's oceans

Oceanic marine creatures are infected by RNA viruses.

Numerous strange viruses that have lately been found hiding in the world's seas may have a significant impact on ecosystems by, among other things, "reprogramming" the hosts they infect.

The latest study, which was released on June 9 in the journal Science, focuses on viruses that include RNA, a molecular relative of DNA. Human illness is rife with RNA viral examples; for example, coronaviruses and influenza viruses are both RNA-based. But when it comes to the diversity of RNA viruses that may be detected and the variety of hosts they can infect, scientists are still learning about them.

According to the new research, "we are certainly sure that most RNA viruses in the ocean are infecting microbial eukaryotes, so fungi and protists, and to a lesser extent, invertebrates," co-first author Guillermo Dominguez-Huerta told Live Science. At the time of the study, Dominguez-Huerta was a postdoctoral scholar in viral ecology at Ohio State University (OSU). Eukaryotes are creatures with intricate cells that have a nucleus where their genetic material is stored.

These protists and fungi, which include algae and amoebas, are the viral hosts that draw carbon dioxide out of the atmosphere and hence affect how much carbon is stored in the ocean. According to Steven Wilhelm, the principle investigator of the Aquatic Microbial Ecology Research Group at the University of Tennessee Knoxville, who was not involved in the current study, RNA viruses certainly have an impact on how carbon moves through the ocean as a whole by infecting these species.

70,000 previously unknown viruses discovered in the human intestine are related.

"Given the abundance of RNA virus particles, knowing they can do this continues to build the story of how important viruses are in the world with respect to how energy and carbon flow," Wilhelm wrote in an email to Live Science.

(Wilhelm has worked on non-study-related projects with Matthew Sullivan and Alexander Culley, two of the study's authors.)

Viruses are present everywhere.

More than 5,500 previously unnamed RNA viruses were discovered in the waters of the world earlier this year, according to Dominguez-Huerta and his colleagues.

The Tara seas Consortium, an ongoing worldwide research exploring the effects of climate change on seas, had gathered 35,000 water samples from 121 sites in the five oceans for that study, which was published April 7 in the journal Science. Plankton, which are microscopic creatures that float in the current and frequently act as hosts for RNA viruses, were abundant in these water samples. The researchers combed through all of the RNA in the plankton cells to uncover a particular sliver of genetic material known as the RdRp gene in order to identify the viruses within these plankton.

The RdRp gene is absent from cells and other viruses, yet it is the sole coding sequence that is shared by all RNA viruses, according to Dominguez-Huerta, a scientific consultant for the company Virosphaera.

In the end, the scientists discovered so many RNA viruses hidden inside the plankton that they advocated tripling the number of RNA virus phyla — the wide taxonomic category just below "kingdom" — from five to ten in order to describe them all.

The researchers then sought to learn more about the hosts that these viruses affect as well as their global distribution.

The researchers found that the viral populations could be divided into four main regions: the Arctic, Antarctic, Temperate and Tropical Mesopelagic, which is between 656 and 3,280 feet (200 and 1,000 meters) under the ocean's surface, and the Temperate and Tropical Epipelagic, which is near the ocean's top. Interestingly, despite a broader range of hosts to infect in warmer seas, the diversity of viruses tended to be highest in the polar regions.

"Viruses, when it comes to diversity, didn't really care about how cold the water is," said Ahmed Zayed, co-first author and research scientist in the OSU Department of Microbiology. According to Zayed, this discovery suggests that several viruses likely fight for the same hosts close to the poles.

The team employed a variety of techniques to identify these viral hosts, including comparing the genomes of RNA viruses with known hosts to those of the newly discovered viruses and looking for infrequent viral RNA remnants in the genomes of host cells, where these remnants of RNA can occasionally be found. This investigation showed that a significant portion of the ocean's RNA viruses infect bacteria, a small percentage infects invertebrates, and many infect fungus and protists.

According to Dominguez-Huerta, the scientists unintentionally found that 95 of the viruses had genes that they had "stolen" from their host cells. These genes aid in controlling cellular metabolism in the host. The scientists concluded that this finding shows that the viruses interfered with the metabolisms of their hosts in some way, perhaps to increase the creation of new virus particles.

Dominguez-Huerta highlighted that earlier, smaller-scale investigations had offered some evidence for this gene-swiping capability.

The team found that 1,200 of the ocean viruses might be involved in carbon export, which is the process by which carbon is taken from the atmosphere, incorporated into marine organisms, and then "exported" to the deep sea as those organisms sink to the seafloor after death. This conclusion was reached after identifying what hosts the ocean viruses are likely to infect.

According to the Monterey Bay Aquarium Research Institute, the longer these carbon reserves are retained in the water before being cycled back into the atmosphere, the deeper they sink. Because of this, scientists take into account carbon export as a key component in climate change models. Because RNA viruses change the cellular activity of their hosts, the current study hypothesizes that the infection of marine species by these viruses may be another, previously unrecognized component driving carbon flow in the seas.

Since RNA viruses frequently burst out of their hosts after quickly multiplying inside them, Wilhelm suggested that RNA viruses may likewise drive carbon flow by rupturing their hosts open and releasing stored carbon into the ocean.