Viral Infections Boost Ocean Productivity and Oxygen Levels in the Sargasso Sea, Study Finds
An international research team, co-led by the University of Tennessee, Knoxville, and the University of Maryland, has published significant findings detailing how viral infections of blue-green algae in the Sargasso Sea enhance ecosystem productivity and contribute to increased oxygen levels. The study, published in Nature Communications, identified a direct link between viral activity and the recycling of carbon and nutrients.
The study identified a direct link between viral activity and the recycling of carbon and nutrients, which stimulates microbial growth and oxygen production within specific oceanic bands.
Background: The Unseen Influence of Marine Viruses
Marine viruses are microscopic organisms, typically tens of nanometers in diameter. Historically, their ecological relevance in marine environments was underestimated. However, advances in transmission electron microscopy in the late 1980s revealed that seawater contains tens of millions of viruses per milliliter, a significantly higher abundance than previously thought.
Most marine viruses infect microorganisms, such as bacteria and algae, which form the base of the ocean's food web and contribute to approximately half of the planet's oxygen generation.
Most marine viruses infect microorganisms, such as bacteria and algae, which form the base of the ocean's food web and contribute to approximately half of the planet's oxygen generation.
The Viral Shunt Model: A Key Ecological Process
The "viral shunt model," first described by Steven Wilhelm and Curtis Suttle in 1999, proposes that marine viruses lyse (break open) microorganism cells. This process releases carbon and nutrients back into the water.
This release is hypothesized to increase nutrient availability for marine phytoplankton, which in turn support krill, fish, and larger marine life, thereby underpinning global fisheries and aquaculture. The new study established a direct connection between this model and the microbial loop within the ocean's food web.
The "viral shunt model" proposes that marine viruses lyse (break open) microorganism cells, releasing carbon and nutrients back into the water.
The Study: Unraveling Viral Impact in the Sargasso Sea
The research was conducted by an international team, co-led by Steven Wilhelm of the University of Tennessee and Joshua S. Weitz of the University of Maryland. In October 2019, researchers undertook a National Science Foundation cruise to the Sargasso Sea.
During this expedition, the team conducted around-the-clock RNA sequencing surveys of the microbiology at the Bermuda Atlantic Time-series Study site, an area that has collected oceanographic data for nearly four decades. Samples were specifically collected from an oxygen-rich band in the subtropical Atlantic Ocean's Sargasso Sea, a region characterized by the dominance of single-celled cyanobacteria, Prochlorococcus.
Key Findings: Direct Evidence of the Viral Shunt
The research provided direct observation of the viral shunt in action. Key findings include:
- The rate of viral infection in the sampled oxygen-rich band was approximately four times higher than in surrounding ocean areas.
- Widespread viral infections were observed in Prochlorococcus populations.
- These viral infections led to the lysis of Prochlorococcus cells, resulting in the release of organic matter and nutrients into the water.
- This released organic matter was subsequently taken up by other bacteria.
- These bacteria then respired carbon and released nitrogen in the form of ammonium.
- The released nitrogen appeared to stimulate further photosynthesis and growth of Prochlorococcus cells, which contributed to the generation of an oxygenated water band. This band, observed 50 meters below the ocean surface, can be meters-wide to meters-thick, extend for hundreds of miles, and persist for several months annually.
- The study concluded that viral infection exerted an ecosystem-scale impact by enhancing nutrient recycling and primary production.
The study concluded that viral infection exerted an ecosystem-scale impact by enhancing nutrient recycling and primary production.
Broader Implications: Global Environmental Significance
The research contributes to the understanding that viruses play a significant role in ecosystem function, including the recycling of carbon and nutrients within ocean environments.
Understanding these microscopic mechanisms is considered essential for monitoring and responding to environmental changes on a global scale.
Understanding these microscopic mechanisms is considered essential for monitoring and responding to environmental changes on a global scale.
Research Team and Funding
The study was published in Nature Communications. Lead authors included Naomi Gilbert and Daniel Muratore. Senior authors were Steven Wilhelm, a professor at the University of Tennessee's Department of Microbiology, and Joshua S. Weitz, a biology professor from the University of Maryland.
Other University of Tennessee authors included Professor Alison Buchan, Assistant Professor Gary LeCleir, Professor Jennifer DeBruyn, and former students Helena Pound and Shelby Cagle. Collaborating institutions included the Georgia Institute of Technology, Ohio State University, and Technion Institute of Technology in Israel. The study received funding from a National Science Foundation Collaborative Research grant, with additional support from the Simons Foundation and other organizations.