A re-post of an article that appeared in January at Inside Science:

Viruses control their hosts like puppets — and in the process, they may play important roles in Earth’s climate.

The hosts in this case aren’t people or animals: They are bacteria. A growing body of research is revealing how viruses manipulate what bacteria eat and how they guide the chemical reactions that sustain life. When those changes happen to a lot of bacteria, the cumulative effects could potentially shape the composition and behavior of Earth’s oceans, soil and air.

“We think that viruses have this huge impact that we just don’t know about,” said Gary Trubl, a soil virus ecologist at Lawrence Livermore National Laboratory in California. “They can actually impact the environment.”

Viruses are basically genetic material packed in a protein shell. To reproduce, they attach to a living cell and inject their genetic material. Some viruses then linger in the cell, often stitching their own DNA into that of the host and being copied along with the host DNA when the cell divides. At some point in a typical viral life cycle, the virus hijacks the cell’s machinery to build new viruses, eventually causing the cell to burst and spill its infectious contents.

It’s debatable whether viruses are alive, but if they are, they are the most abundant organisms on the planet. Most are so small it would take 55 million of them to cover the period at the end of this sentence, according to a review by Mya Breitbart and colleagues at the University of South Florida. But if you strung all the viruses in Earth’s oceans together end to end, they could span the distance to Mars and back 12 trillion times.

The vast majority of viruses infect bacteria.

“If you go swimming in the ocean, that’s about 200 million viruses per every mouthful of seawater. And almost all of those are going to be infecting the 20 million bacteria in that same mouthful of seawater,” said Jennifer Brum, an oceanographer at Louisiana State University in Baton Rouge.

Viral infections are a ubiquitous part of bacterial life. This is a big deal, since bacteria recycle and transform the chemicals we eat and breathe. When viruses kill bacteria, they release nutrients back into the environment. Recently, scientists have been finding that viruses also change what bacteria do while they’re alive.

“We live in a bacteria-driven world,” said Martha Clokie, a microbiologist at the University of Leicester in the U.K. “Those bacteria are endlessly being subtly manipulated by viruses.” [Continue reading…]