Missing Link Between Viruses and Cells Found

Researchers have discovered two new giant viruses they say blur the lines between viruses and cells.

Published in the journal Science, the first, called the Pandoravirus salinus, was discovered off the coast of Chile, while the second, Pandoravirus dulcis, was found in a freshwater pond in Melbourne, Australia.

Detailed analyses of both reveal the two share nothing with previously characterized giant viruses; moreover, only 6 percent of proteins encoded by Pandoravirus salinus represent anything similar to those in other viruses or organisms. Its massive genome, the researchers explain, shows that viruses are capable of being more complex than some eukaryotic cells.

Both Pandoraviruses lack a gene enabling them to build a protein similar to the capsid protein, considered an essential part of traditional viruses. Nevertheless, the absence of a ribosome, inability to produce energy or divide all ensure the title of virus for both.

Included in the analysis is the Pandoravirus salinus proteome. Derived from the words "protein" and "genome," a proteome refers to all of the proteins an organism produces. The results showed that the the virus's proteins are consistent with those predicted by its genome sequence, according to the researchers, indicating that Pandoraviruses use the same genetic code as all other living organisms.

According to the press release outlining the study, "This shows just how much more there is to learn regarding microscopic biodiversity as soon as new environments are considered."

The fact that the specimens were discovered simultaneously and 15,000 kilometers apart indicates that Pandoraviruses are not entirely unique, despite being completely unknown until now. 

"It definitively bridges the gap between viruses and cells -- a gap that was proclaimed as dogma at the very outset of modern virology back in the 1950s," the press release continues. "It also suggests that cell life could have emerged with a far greater variety of pre-cellular forms than those conventionally considered, as the new giant virus has almost no equivalent among the three recognized domains of cellular life, namely eukaryota (or eukaryotes), eubacteria, and archaea."