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"Choosy" Virus

23 April 2015

For the most part, evolution seems a lot like a lottery of mutations. The winners get to survive, reproduce, and eventually evolve. The losers disappear from all but the fossil record. Now new research has revealed that a small group of microbes and viruses are apparently cheating the system, systematically picking and choosing what mutates to help them live in some hostile environments.

At the deepest nooks and crannies of our ocean floors, you can find some remarkable and unusual life forms. This certainly is true of archaea, primitive single-celled bacteria-like microorganisms that many believe have been around for billions of years.

Archaea have been seen as extremely resilient organisms, where those that live in the most punishing of environments - where little other life can be found - are called extremophiles.

However, even the most remote and extreme habitat is no refuge from infection. A team of researchers from the University of California, Santa Barbara (UCSB) recently discovered a remarkable virus that seemingly infects methane-eating archaea living at incredibly deep depths off the coast of Santa Monica, Calif. More amazing still, this virus seems to have the ability to selectively target one of its own genes for mutation, allowing it to survive alongside its host despite an oppressive environment.

"Our study illustrates that self-guided mutation is relevant to life within the Earth's subsurface and uncovers mechanisms by which viruses and archaea can adapt in this hostile environment," David Valentine of UCSB said in a recent statement. "These findings raise exciting new questions about the evolution and interaction of the microbes that call Earth's interior home."

These findings were detailed in the journal Nature Communications.

"It's now thought that there's more biomass inside the Earth than anywhere else, just living very, very slowly in this dark, energy-limited, starved environment," she explained.

According to the study, Bagby and her colleagues used genetic sequencing of the newly discovered virus to determine just what its host is. After all, viruses do not last long in the outside world - whether it be the harsh realm of the deep sea or a comfortable home office. They also compared its genetic fingerprint to those found in a global database.

"We found a partial genetic match from methane seeps in Norway and California," said lead author Blair Paul, also of the Valentine lab. "The evidence suggests this viral type is distributed around the globe in deep ocean methane seeps" - likely affecting archaea for nearly as long as they have been around.

So what has kept this virus going? Like with the flu or other common bugs, the virus can rapidly mutate to adapt to changes in its host's defenses. However, under the extreme pressures of their home, the extremophiles have become exceptionally resilient organisms, certainly capable of out-adapting one measly virus.

The researchers found that to keep pace, the virus has somehow bent the rules on adaptation. At 'will,' the virus can prompt and accelerate mutation, and on top of that, it is also capable of selecting what part of its genome will change.

Paul compared the moment when the virus tries to find its way into an archaea's cell to a "genetic arms race," in which both resilient parties are rapidly mutating to outmatch the other. Now the researchers suspect that the extremophiles themselves may use the same rule-bending technique to keep the virus at bay and even adapt to its harsh and punishing home.

"The cell is choosing to modify certain proteins," Valentine explained. "While we don't know what those proteins are being used for, I think learning about the process can tell us something about the environment in which these organisms thrive. Right now, we know so little about life in that environment."

But, his team added, the hope is that this will soon change.

First published in Nature World News