Imagine a world beneath the waves where invisible viruses play a vital role in shaping the ocean's oxygen levels—an idea that challenges traditional notions of harmful microorganisms. Recent groundbreaking research from the University of Tennessee, Knoxville, in collaboration with the University of Maryland, reveals that viral infections of blue-green algae in the ocean actually boost productivity and help create a substantial oxygen-rich zone beneath the surface waters.
This study underscores that our planet's marine environment is a bustling microbial universe, where viruses aren’t just agents of disease—they are integral players that can stimulate growth and ecosystem vitality. As Steven Wilhelm, a leading microbiologist at UT and one of the project's senior scientists, explains: “We live on a microbial planet, and viruses are part of that intricate web.” Sometimes, instead of causing harm, these viruses kickstart processes that make the ocean more productive.
The research was directed by Wilhelm during a scientific expedition aboard the Atlantic Explorer research vessel in October 2019. This cruise was part of the long-term Bermuda Atlantic Time-series Study, a continuous effort spanning nearly forty years that collects a wide array of physical, biological, and chemical ocean data. During this expedition, the team carried out around-the-clock RNA sequencing to analyze the tiny microbes living in the water.
Significantly, the new findings demonstrate that when viruses infect the cyanobacterium Prochlorococcus—a key contributor to oceanic photosynthesis—they release nutrients that fuel the growth of other microorganisms. This process contributes to increased oxygen levels in water layers roughly 50 meters below the surface, creating a 'living ribbon' of oxygenated water that persists for months each year.
And here’s where it gets controversial… the study highlights a direct connection between two fundamental concepts in ocean science: the 'viral shunt,' a term first introduced by Wilhelm and Curtis Suttle in 1999, and the microbial loop that sustains the ocean’s food web. The viral shunt describes how viruses break open microbial cells, releasing nutrients back into the environment, thus recycling essential elements. This process supports the microbial loop, which keeps nutrients flowing and boosts ocean productivity.
By analyzing large datasets of viral and cellular activity across day-night cycles, Professor Joshua S. Weitz from the University of Maryland, explains that viral infections leave an identifiable imprint on the entire ecosystem. These infections enhance the recycling of carbon and nutrients through other microbes, which boosts overall productivity and offers fresh insights into how viruses influence ocean health below the surface.
The RNA sequencing work and further analyses were carried out at UT, with prominent contributions from Dr. Naomi Gilbert, the lead author, along with microbiology professors Alison Buchan and Gary LeCleir, and Professor Jennifer DeBruyn from the Department of Biosystems Engineering and Soil Science. The project was funded by a National Science Foundation grant, supported additionally by the Simons Foundation and other organizations.
Wilhelm and Weitz plan to share their findings more broadly through an upcoming discussion in The Conversation—making complex ocean processes accessible to everyone.
This research, titled 'Seasonal enhancement of the viral shunt catalyzes a subsurface oxygen maximum in the Sargasso Sea,' was published in Nature Communications on December 6, 2025. It raises intriguing questions about the nuanced roles viruses play in ecosystems—are they simply agents of destruction, or essential catalysts for planetary health? What are your thoughts on this perspective? Do you agree that viruses could be nature’s unsung heroes in maintaining the ocean’s oxygen levels? Feel free to share your opinions—this is a conversation worth having.
