Giant Viruses Blur Line Between Life and Virus

Viruses are normally tiny, spreading through their hosts as they replicate. Now, though, scientists have uncovered giant viruses from sludge across the world. The new findings have blurred the line between life and viruses which, at present, are not considered to be living beings.

One of the new viruses was first discovered off of the coast of Chile. About the size of a small bacterial cell, it appeared to be infecting and killing amoebae. A similarly large virus was discovered in a pond in Australia. With genomes topping out at 1.9 million and 2.5 million bases, respectively, these viruses are larger than any yet discovered--and are even bigger than many bacteria and even some eukaryotic cells.

"This is a major discovery that substantially expands the complexity of the giant viruses and confirms that viral diversity is still largely underexplored," said Christelle Desnues, a virologist at the French National Centre for Scientific Research, who was not involved in the study in an interview with Nature.

Normal viruses are about 20 to 300 nanometers in size. In addition, many of these viruses, such as HIV and influenze, have 10 or fewer genes. Needless to say, these giant viruses are absolutely enormous in comparison, according to Discovery News.

"We were prepared to find new viruses in the 1,000-gene range, but not to more than double that figure," said Chantel Abergel, one of the researchers, in an interview with Discovery News. "This really indicates that we don't know what are the possible limits anymore."

The two new viruses are called Pandoravirus salinus and Pandoravirus dulcis. They both attack amoebas after they're engulfed by them. The nucleus of the amoebas begins transforming radically and ultimately vanishes. When the amoebas finally die, they release about 100 pandoraviruses.

Currently, the researchers are trying to determine the viruses' origins by characterizing the unknown genes and proteins that they encode. It's very possible that they evolved from cells; if that's true, then the ancestors of Pandoraviruses must have been very different from the bacteria, archaea and eukaryotes of today.

"I think it's wonderful that such crazy and divergent lifeforms continue to be discovered," said Tom Williams of Newcastle University in an interview with the NY Times.

The findings are published in the journal Science.