In the chilly depths of one of Antarctica's freshwater lakes, a surprising number of novel viruses thrive.

Researchers braved frigid temperatures to collect water samples from Lake Limnopolar, located on Livingston Island near the Antarctic Peninsula, and sequenced the genomes of the collected species. The new genetic study reveals some 10,000 species of viruses from a dozen families.

The viral diversity in the surface lake was "unexpectedly high," the authors wrote in a report on their findings, published online Thursday in Science. Most aquatic environments typically are home to viral species from only three to six families. The authors attribute the "unprecedented taxonomic diversity and high genetic richness" to the low diversity of other organisms at the site.

These extremophiles survive by living in the lake's eukaryotes, subsisting through nine months of low-nutrient—and dim-light—levels. They are closely related to viruses that infect larger animals and plants rather than more common aquatic bacteriophages that infect prokaryotes.

The researchers also compared samples taken at different times of the year and found that come high summer (December in Antarctica), when the ice melts away from the lake's surface, many of the single-stranded DNA viruses had changed into double-stranded versions. "It looks like a completely different lake in the summer," noted Antonio Alcami, of the Spanish Research Council and co-author on the study, reported.

In fact, some of these more complex viruses may be changing to help their hosts thrive and adapt to a sunnier summer environment, which in turn helps the viruses proliferate. The viruses were found, for example, to contain genes involved in photosynthesis, which might help their algae hosts bloom in the summer.

"We are just starting to uncover the world of viruses," Alcami said. "And this is changing the way we think about viruses and the role they play in microbial ecosystems."

Image of researcher sampling lake water courtesy of Science/AAAS