Marine viruses are critical to sustain our ecosystem

Photo by Matthias Fischer

When thinking of viruses, particularly in the current context where COVID-19 is impacting lives in multiple ways, they are seen as spreaders of disease.

However, Curtis Suttle, professor in environmental virology at the University of British Columbia (UBC), reveals another reality. “What we don’t recognize is that we couldn’t exist without them,” he says. “They are critically important to keep us alive and the ecological system functioning. For the most part, viruses are not our enemy.”

He points out that more than 95% of the living material in the oceans are microbes, which produce about half of the earth’s oxygen. Every day, viruses kill 20% of that living material by weight. They are therefore a critical part of continuing the ocean’s processes, and impact global biogeochemical cycling in terms of nutrients and oxygen and carbon dioxide.

Some facts about viruses

Curtis Suttle, professor in environmental virology at the University of British Columbia. | Photo by Henry Lam, Hong Kong University of Science and Technology

Suttle explains that viruses likely arose around four billion years ago from the same material that created cellular life. Essentially, viruses consist of genetic material inside a small protein shell. To give a sense of viruses’ minute size, Suttle calculates that if we made a virus into something we could see, such as a pinhead, and he scaled himself by the same amount, he would be 150,000 feet tall!

Viruses are tiny but abundant. Hundreds of millions of viruses can be found in one teaspoon of sea water. “If you take the minimum estimate of the total number of viruses in the ocean and stretch them all from end to end in a long string, they would go further than the nearest sixty galaxies,” Suttle says.

Viruses cannot replicate unless they infect an appropriate host. A crucial characteristic of viruses is that they are host specific. “Every time we go swimming, for example, we swallow as many viruses as there are people in North America,” Suttle notes. “But they don’t make us ill, because they are not viruses which infect us.”

Viruses regulate biodiversity

Suttle’s interest in the topic began at age twelve, while on a four-year sailing trip around the world with his family. While sailing up the Great Barrier Reef, the family discovered a research vessel where scientists were studying marine life. This experience sparked Suttle’s lifelong interest in biodiversity and why there are so many different types of life in the ocean. In the late 1980s these questions led him to focus specifically on viruses and their interactions with organisms and the ocean’s plankton and bacteria, then an unstudied area. Scientific papers had stated the ocean contained few viruses. “As it turns out, viruses are really important,” Suttle says.

Cyanophage – Electron micrograph of marine viruses. | Photo by Amy M Chan, University of British Columbia

According to the magazine Nature, between 2009 and 2013, seawater samples were collected from almost 80 sites around the world as part of Tara Oceans and Malaspina projects. These initiatives focused on the study of carbon dioxide and climate change in the earth’s oceans. 200,000 virus populations were found in five ocean zones, twice the amount previously recorded by scientists. Matthew Sullivan, senior author on the study and a microbiologist at Ohio State University emphasized that this new map of virus diversity could allow scientists to manipulate specific areas of the ocean so that the viral community could move more carbon dioxide from shallow waters into the deep ocean. This would lock carbon dioxide away from the atmosphere.

Suttle elaborates that most microbes are surrounded by hard “walls” of organic carbon, somewhat like wood. When viruses kill these microbes, some of this material is left behind, and will not be degraded for thousands of years. “If we can increase the rate at which viruses are killing material in the ocean, we could build up this storehouse of organic carbon. As the original source of this carbon is carbon dioxide, it has the effect of reducing its buildup in the atmosphere,” he says. This idea is captured by “The Shunt and Pump,” a concept proposed by Suttle to describe how viruses can contribute to sequestering and storing carbon.

Future research areas

Chrysovirus viroplasm – Electron micrograph of a virus-infected phytoplankton. The dark hexagonal shapes are individual virus particles inside a phytoplankton cell. | Photo by Amy M Chan, University of British Columbia

Suttle believes further viral research is needed, as nothing is known about the role of viruses in regulating fish populations or different kinds of plankton in the ocean. A crucial aspect is learning about the effects of viruses on the health and survival of salmon. A recently published paper highlights the discovery of a virus related to the one that causes COVID-19 in salmon. “This won’t infect humans, but it’s a relative and the first one ever found in fish,” Suttle clarifies. “It’s a huge opportunity to explore what viruses are doing in the system. That’s just one piece. We have no idea what their effect is on herring, another commercially important fish. And if we get into things that aren’t commercially important, nobody’s even looked.”

Research also needs to be done on the role of viruses in regulating zooplankton populations, as well as how they interact with specific species and their impact on those populations.

Suttle reiterates the longstanding importance of viruses as part of our ecosystem. “With every breath, we breathe in thousands of viruses; they don’t make us sick and might be really important in terms of health because they may infect bacteria that would make us sick. Occasionally, we get broadsided by some disease that sweeps through our populations and can have a major impact, but for the most part, we’re really dependent on viruses and what they do.”

To learn more about Suttle’s research, visit www.eoas.ubc.ca/people/curtissuttle

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