New study probes effects on global nutrient cycling

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New study probes effects on global nutrient cycling

Can viruses affect the climate

Nowadays, we are increasingly accustomed to the idea that entire ecosystems of tiny bacteria live on our skin, in the soil of our gardens and in the oceans where we eat.

But one aspect that has remained under-explored is the ecosystems of these ecosystems. Bacteria also contract viruses - and new research by scientists at the University of Chicago is exploring the role these viruses can play in the gigantic global recycling system that makes up the planet's climate.

"There are ten billion viruses in every liter of seawater. We've known this for at least 20 or 30 years, but we have very little idea of what they do and how they affect global carbon cycles," said Maureen Coleman, co-principal author, assistant professor of geophysical sciences whose innovative research focuses on the interactions between microbes, ecology and climate.

In a new study published on 15 July in the Proceedings of the National Academy of Sciences, scientists showed that cyanobacteria infected with viruses continue to extract nitrogen from the environment and channel it into the production of new viruses. This is an important discovery in the emerging field of what is called viral biogeochemistry, the way viruses shape the movement of nutrients in air, water and soil, and thus the earth's climate.

Bacteria are the reason we are here. Once upon a time, they transformed the earth from an empty and austere world into a quiet and patient photosynthesis of oxygen for billions of years. They still play a huge role in the planet's climate, displacing nitrogen, carbon and other nutrients in and out of the atmosphere and oceans.

But because they are so small and so many, there are many things we do not understand. For example, we know that for every bacterial cell, there are tons more viruses - and these viruses infect bacteria, affecting their actions and competing for nutrients. For example, viruses divert biosynthesis plants from a cell and force them to make more copies of the virus, which are then released to spread infection. How does this affect the absorption of carbon or other important nutrients by the cell?

The researchers wanted to know how viruses would change the use of nitrogen by bacteria, a key nutrient in all cells. They started with a particularly large class of bacteria called cyanobacteria, which live in oceans and waters around the world and are a huge part of the world's photosynthesis and carbon fixation.

"Half of carbon sequestration occurs in the oceans, and cyanobacteria play an extremely important role in this cycle," said Jacob Waldbauer, Assistant Professor to the Neubauer family and co-lead author of the study. "We need a basic understanding of what affects their function and productivity, and we know very little about the role viruses play."

To learn more, the researchers fed the cyanobacteria with nitrogen, infected some of them with viruses, and then placed them in a bath containing another type of nitrogen. This meant that they could accurately track the amount of nitrogen absorbed by the cell after it was infected, and where it was used.

The results were clear: the infected bacteria absorbed a large amount of nitrogen. All this was used to make more viruses - none were used to make proteins for the host cell.

Previously, Coleman said, many assumed that viruses simply cannibalize nutrients from their host cells. "We didn't appreciate the fact that he also gets nutrients from the environment for his own needs," she says. "It is clear that the virus reprograms host cells in a way that could affect the fate of nutrients in the system."

There is much more to explore, the researchers said. For example, they want to know if an infected cell absorbs more nitrogen than a healthy cell, if different types of viruses have different effects and how temperature affects the whole body, which is important as the oceans warm.

"There's a lot more to tell," Coleman said. "But even from this study, it is clear that they are changing the way ecosystems use nutrients - and that we need to know how if we are to fully understand climate.