“Huge discoveries remain to be made at the most fundamental level that may change our present conception about the origin of life and its evolution,” says virologist Jean-Michel Claverie, a coauthor of a seminal study, which has been published in this week’s issue of the journal Science.
There are three known domains of life: Bacteria; Archaea, another type of single-celled organism; and Eukaryotes. Scientists believe they may have discovered a fourth domain, a distinct, previously unknown branch of life. A study by the French National Research Agency at Aix-Marseille University that has uncovered two gigantic viruses dubbed “Pandoraviruses” because of the surprises they may hold for biologists -a reference to Pandora, the mythical Greek figure who opened a box and released evil into the world.
Our knowledge of Earth’s microbial biodiversity is still incomplete, says Claverie, who theorizes that the ancient ancestors of Pandoraviruses were once free-living cells that gradually lost most of their genes as they became parasitic. Pandoraviruses may expand our knowledge of life on Earth because they represent a fourth domain of microbial organisms.
One of the viruses, Pandoravirus salinus, was unearthed from sediments collected off the coast of Chile. The other, Pandoravirus dulcis, was discovered in a freshwater pond near Melbourne, Australia. “The fact that two of them were found almost simultaneously from very distant locations either indicate that we were incredibly lucky,” Claverie said, “or that they are not rare.”
In the beginning of their study, the French scientists thought both viruses were the same until they compared the two genome sequences and their encoded proteins, when they realized that the pair represented a new virus family, said Claverie.
To confirm that Pandoraviruses were indeed viruses, the researchers used light and electron microscopes, following their newfound entities through a complete replication cycle. The strange entities met all three key criteria to be labeled viruses.