Scientists Have Long Believed That Ocean Viruses Always Quickly Kill Algae – They Were Wrong

This image depicts viral infection of an Emiliania huxleyi cell superimposed on a satellite image of an E. huxleyi bloom in the Barents Sea.
Credit: MODIS, NASA; Steve Gschmeissner, Photo Researchers Inc.; Kay Bidle & Christien Laber, Rutgers University

Ocean algae get ‘coup de grace’ from viruses. Viruses don’t immediately kill algae but live in harmony with them.

Scientists have long believed that ocean viruses always quickly kill algae, but Rutgers-led research shows they live in harmony with algae and viruses provide a “coup de grace” only when blooms of algae are already stressed and dying.

The study, published in the journal Nature Communications, will likely change how scientists view viral infections of algae, also known as phytoplankton — especially the impact of viruses on ecosystem processes like algal bloom formation (and decline) and the cycling of carbon and other chemicals on Earth.

“It’s only when the infected algal cells become stressed, such as when they run out of nutrients, that the viruses turn deadly,” said lead author Benjamin Knowles, a former post-doctoral researcher in the Department of Marine and Coastal Sciences in the School of Environmental and Biological Sciences at Rutgers University-New Brunswick who is now at UCLA. He was also a post-doctoral fellow at Rutgers’ Institute of Earth, Ocean, and Atmospheric Sciences. “We feel that this entirely new model of infection is widespread in the oceans and stands to fundamentally alter how we view host-virus interactions and the impact of viruses on ecosystems and biogeochemical cycling since it goes against the long-accepted classic model of viruses always being lethal and killing cells.”

Biogeochemical cycling refers to essential nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, iron and water circulating through organisms and the environment. The coccolithophore algae Emiliania huxleyi was the focus of the study as a model for other algae-virus systems and is a central driver of this process.

The scientists studied virus-algae interactions in the lab and in controlled, mini-blooms in coastal waters of Norway. They focused on viral infection of a form of algae that is responsible for generating much of the oxygen and carbon cycling on Earth. A group of ocean viruses called coccolithoviruses routinely infect and kill E. huxleyi over 1,000 square miles, which is viewable from space via Earth-observing satellites.

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