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Viruses often conjure images of illness and outbreaks, yet in the vastness of the ocean, some viruses play a crucial role in sustaining marine life. A new study sheds light on how these microscopic entities contribute to the marine food web, revealing their unexpected importance.
In a groundbreaking study, an international team of scientists, including researchers from the University of Tennessee and the University of Maryland, explored the behavior of marine viruses in a large band of oxygen-rich water just beneath the surface of the Atlantic Ocean. Their findings, published in Nature Communications, highlight the pivotal role these viruses play in the ocean’s ecosystems.
Unveiling the Invisible: The World of Marine Viruses
Viruses are incredibly small, often no more than tens of nanometers in diameter, making them nearly a hundred times smaller than bacteria and over a thousand times smaller than a human hair. This minuscule size means they cannot be observed using conventional microscopes. For decades, scientists underestimated their abundance and ecological significance in marine environments.
The late 1980s marked a turning point with advancements in transmission electron microscopy, allowing scientists to observe sea water at high magnification. They discovered tens of millions of viruses per milliliter of water, a figure tens of thousands of times greater than previously estimated.
The Viral Shunt: Feeding the Ocean
Marine viruses primarily infect microorganisms such as bacteria and algae, which form the base of the ocean food web and are responsible for approximately half of the planet’s oxygen production. By the late 1990s, scientists hypothesized that viral activity significantly influences the cycling of carbon and nutrients in ocean systems.
“We hypothesized, in what’s known as the viral shunt model, that marine viruses break open the cells of microorganisms, releasing their carbon and nutrients into the water.”
This process, known as the viral shunt, increases the availability of nutrients to marine phytoplankton, which in turn feed krill and fish, supporting larger marine life. This intricate web is vital to the global fisheries and aquaculture industry, which produces nearly 200 million metric tons of seafood annually.
Observing Viruses in Action
The recent study, led by biologists Naomi Gilbert and Daniel Muratore, demonstrated the viral shunt in action. The team collected samples from a meters-thick band of oxygen that stretches for hundreds of miles across the subtropical Atlantic Ocean, part of the Sargasso Sea. Here, single-celled cyanobacteria known as Prochlorococcus dominate marine photosynthesis, with up to 100,000 cells per milliliter of seawater.
Using RNA sequencing, researchers observed the interactions between viruses and their hosts. They found that the rate of viral infection in this oxygen-rich band is about four times higher than in surrounding ocean areas, where cyanobacteria reproduce more slowly. The study revealed massive viral infections in Prochlorococcus, leading to the release of organic matter that bacteria consume, fueling their growth.
“The viral infection was having an ecosystem-scale impact, stimulating photosynthesis and the growth of more Prochlorococcus cells, resulting in greater oxygen production.”
Implications for Ecosystem Understanding
While viruses can have severe impacts on human and animal health, this research highlights their essential role in ecosystem functioning. Supported by the National Science Foundation, the study adds to a growing body of work demonstrating that viruses are central to processes such as carbon storage in the deep oceans.
As the planet undergoes rapid changes, understanding the microscopic world and its mechanisms is crucial for monitoring and responding to environmental shifts. This study serves as a reminder of the importance of exploring the unseen life of viruses that shape the fate of microbes and influence Earth’s systems.
Steven Wilhelm, Professor of Microbiology at the University of Tennessee, and Joshua Weitz, Professor of Biology at the University of Maryland, contributed to this research. Their work underscores the need for continued exploration of the microscopic world to better understand global ecological processes.
The Conversation, an independent and nonprofit source of news, analysis, and commentary from academic experts, provided the original report.
