Viruses might often be associated with sickness and fears of epidemics, but when it comes to our oceans, they can actually be quite beneficial. Recent research reveals that certain viruses play a vital role in supporting marine ecosystems.
In an exciting new study, our team, alongside international scientists, explored the behavior of marine viruses within a broad strip of oxygen-rich water just beneath the surface of the Atlantic Ocean. What we uncovered about these viruses and their contributions to the oceanic food web presents a fresh perspective on their ecological significance.
The Microscopic World of Viruses
Viruses are remarkably tiny, typically measuring only a few tens of nanometers in diameter. To put this into perspective, they are nearly a hundred times smaller than bacteria and over a thousand times narrower than a human hair. This incredible smallness means that conventional microscopes cannot even detect them.
For many years, researchers believed that marine viruses were not very numerous and lacked ecological importance, despite their clear connection to humans, plants, and animals. However, everything changed when advancements in transmission electron microscopy emerged in the late 1980s. Scientists could then scrutinize seawater at extraordinarily high magnifications and discovered countless minute circular entities containing DNA—these were viruses. Astonishingly, there were tens of millions of these viruses present in every milliliter of seawater, far surpassing previous estimates.
Viruses: Key Players in the Marine Food Web
Most marine viruses target the cells of microorganisms like bacteria and algae, which form the foundation of the oceanic food web and account for roughly half of the Earth’s oxygen production. By the late 1990s, researchers began to suspect that the activity of viruses was instrumental in determining how carbon and nutrients cycled through ocean systems. This led to the formulation of the viral shunt model, which posits that marine viruses break open the cells of microorganisms, releasing their carbon and nutrients back into the surrounding waters.
This release of nutrients can enhance the availability of essential resources for marine phytoplankton, the primary food source for organisms like krill and fish, which, in turn, support larger marine species. Consequently, viruses are crucial to the food web that sustains the global fisheries and aquaculture sectors, which collectively yield nearly 200 million metric tons of seafood annually.
Observing Viral Activity in Action
In our recent study published in the journal Nature Communications, led by biologists Naomi Gilbert and Daniel Muratore, we provided direct evidence for the viral shunt hypothesis. We collected samples from a thick band of oxygen that stretches for hundreds of miles across the subtropical Atlantic Ocean, notably part of the Sargasso Sea. In this area, single-celled cyanobacteria known as Prochlorococcus dominate, with concentrations reaching from 50,000 to over 100,000 cells per milliliter of seawater. These Prochlorococcus cells are susceptible to viral infections.
Using RNA sequencing to analyze the genetic material of both viruses and their hosts simultaneously, we discovered that the rate of viral infections in this oxygen-rich region was approximately four times higher than in adjacent areas of the ocean where cyanobacteria do not proliferate as much. We observed significant viral activity causing extensive infections in Prochlorococcus cells.
As viruses attacked these cells, they released organic matter that bacteria could utilize for growth. The bacteria metabolized this carbon and emitted nitrogen in the form of ammonium, which appeared to stimulate photosynthesis and promote the growth of more Prochlorococcus. This chain reaction resulted in an increased production of oxygen, demonstrating the profound impact that viral infections can have on entire ecosystems.
The Importance of Understanding Viruses
While viruses can lead to serious health issues in humans and animals, this new study—facilitated by an open-ocean expedition supported by the National Science Foundation—adds to a growing body of research showcasing the crucial roles that viruses play in ecosystem dynamics, including their contributions to carbon storage in deep oceans.
As our planet undergoes significant changes, tracking and addressing environmental shifts necessitates a comprehensive understanding of the microbes and processes that drive global systems. This study serves as a compelling reminder of the need to delve deeper into the microscopic world, particularly the lives of viruses that influence microbial dynamics and the functioning of Earth’s ecosystems.
