Virus. The word conjures images of illness and fears of outbreaks. However, in the oceans, not all viruses are bad news.
Some play a useful, even critical, role in sustaining marine life.
In a new study, we and an international team of scientists examined the behavior of marine viruses in a large swath of oxygen-rich water just beneath the surface of the Atlantic Ocean. What we discovered there—and their role in the food web—shows marine viruses in a new light.
Study something so small
Viruses are incredibly small, typically no larger than tens of nanometers in diameter, almost a hundred times smaller than a bacteria and more than a thousand times smaller than the width of a strand of hair.
In fact, viruses are so small that they cannot be seen with conventional microscopes.
Decades ago, scientists thought that marine viruses were neither abundant nor ecologically relevant, despite the clear relevance of viruses to humans, plants and animals.
Then advances in the use of transmission electron microscopes in the late 1980s changed everything. The scientists were able to examine the seawater at very high magnification and saw tiny circular objects containing DNA. They were viruses, and there were tens of millions per milliliter of water, tens of thousands of times more than had been estimated in the past.
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A theory about how viruses feed the marine world
Most marine viruses infect the cells of microorganisms, bacteria and algae that serve as the basis of the oceanic food web and are responsible for approximately half of the oxygen generated on the planet.
In the late 1990s, scientists realized that viral activity was likely shaping how carbon and nutrients circulated through ocean systems. We hypothesize, in what is known as the viral derivation model, that marine viruses break down the cells of microorganisms and release their carbon and nutrients into the water.
This process could increase the amount of nutrients reaching marine phytoplankton. Phytoplankton provide food for krill and fish, which in turn feed larger marine life throughout the oceans. That would mean viruses are essential to a food web that powers a vast global fishing and aquaculture industry that produces nearly 200 million metric tons of seafood.
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Watching viruses in action
In the new study published in the journal Nature Communications led by biologists Naomi Gilbert and Daniel Muratore, our international team demonstrated the viral shunt in action.
The team sampled a several-meter-thick band of oxygen that extends for hundreds of miles across the subtropical Atlantic Ocean. In this region, part of the Sargasso Sea, single-celled cyanobacteria known as Prochlorococcus They dominate marine photosynthesis, with about 50,000 to more than 100,000 cells in each milliliter of seawater. These Prochlorococcus They can become infected with viruses.
By sequencing community RNA—molecules that carry genetic instructions inside cells—our team was able to observe what almost all viruses and their hosts were trying to do at once.
We found that the viral infection rate in this oxygen-rich band of ocean is about four times higher than in other parts of the surrounding ocean, where cyanobacteria do not reproduce as quickly. And we observed viruses that caused massive infections in Prochlorococcus.
Viruses attacked cells and shed organic matter, which bacteria absorbed and used to feed new growth. The bacteria respired the carbon and released nitrogen in the form of ammonium. And this nitrogen appears to have been stimulating photosynthesis and the growth of more cells de Prochlorococcuswhich resulted in greater production generated by the oxygen tape.
The viral infection was having an impact on an ecosystem scale.
Understanding the microscopic world is important
Viruses can cause acute, chronic and catastrophic effects on human and animal health. But this new research, made possible by an open ocean expedition supported by the National Science Foundation, adds to a growing range of studies showing that viruses are central players in the functioning of ecosystems, including their role in storing carbon in the deep ocean.
We live in a changing planet. Monitoring and responding to changes in the environment requires understanding the microbes and mechanisms that drive global processes.
This new study reminds us how important it is to further explore the microscopic world, including the life of viruses that shape the fate of microbes and how the Earth system works.
*Steven Wilhelm is Professor of Microbiology at the University of Tennessee and Joshua Weitz is Professor of Biology at the University of Maryland.
This article was originally published on The Conversation
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