Pandoravirus: Missing link discovered between viruses and cells

October 14, 2013, Commissariat a l'Energie Atomique (CEA)

Researchers at IGS, the genomic and structural information laboratory (CNRS/Aix-Marseille University), working in association with the large-scale biology laboratory (CEA/Inserm/Grenoble Alpes University) have just discovered two giant viruses which, in terms of number of genes, are comparable to certain eukaryotes, microorganisms with nucleated cells. The two viruses – called "Pandoravirus" to reflect their amphora shape and mysterious genetic content – are unlike any virus discovered before. This research appeared on the front page of Science on July 19, 2013.

With the discovery of Mimivirus ten years ago and, more recently, Megavirus chilensis, researchers thought they had reached the farthest corners of the viral world in terms of size and genetic complexity. With a diameter in the region of a micrometer and a genome incorporating more than 1,100 , these giant viruses, which infect amoebas of the Acanthamoeba genus, had already largely encroached on areas previously thought to be the exclusive domain of bacteria. For the sake of comparison, common viruses such as the influenza or AIDS viruses, only contain around ten genes each.

In the article published in Science, the researchers announced they had discovered two new giant viruses:

  • Pandoravirus salinus, on the coast of Chile
  • Pandoravirus dulcis, in a freshwater pond in Melbourne, Australia

Detailed analysis has shown that these first two Pandoraviruses have virtually nothing in common with previously characterized . What's more, only a very small percentage (6%) of proteins encoded by Pandoravirus salinus are similar to those already identified in other viruses or cellular organisms. With a genome of this size, Pandoravirus salinus has just demonstrated that viruses can be more complex than some . Another unusual feature of Pandoraviruses is that they have no gene allowing them to build a protein like the capsid protein, which is the basic building block of traditional viruses.

Despite all these novel properties, Pandoraviruses display the essential characteristics of other viruses in that they contain no ribosome, produce no energy and do not divide.

This groundbreaking research included an analysis of the Pandoravirus salinus proteome, which proved that the proteins making it up are consistent with those predicted by the virus' genome sequence. Pandoraviruses thus use the universal genetic code shared by all living organisms on the planet.

This shows just how much more there is to learn regarding microscopic biodiversity as soon as new environments are considered. The simultaneous discovery of two specimens of this new virus family in sediments located 15,000 km apart indicates that Pandoraviruses, which were completely unknown until now, are very likely not rare.

It definitively bridges the gap between and cells – a gap that was proclaimed as dogma at the very outset of modern virology back in the 1950s.

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.

Explore further: Huge viruses may open 'Pandora's' box: French study

More information: "Pandoraviruses: Amoeba viruses with genomes up to 2.5 Mb reaching that of parasitic eukaryotes". Nadège Philippe, Matthieu Legendre, Gabriel Doutre, Yohann Couté, Olivier Poirot, Magali Lescot, Defne Arslan, Virginie Seltzer, Lionel Bertaux, Christophe Bruley, Jérome Garin, Jean-Michel Claverie, Chantal Abergel. Science. DOI: 10.1126/science.1239181

Related Stories

What the smallest infectious agents reveal about evolution

May 22, 2013

Radically different viruses share genes and are likely to share ancestry, according to research published in BioMed Central's open access journal Virology Journal this week. The comprehensive phylogenomic analysis compares ...

Study of giant viruses shakes up tree of life

September 13, 2012

A new study of giant viruses supports the idea that viruses are ancient living organisms and not inanimate molecular remnants run amok, as some scientists have argued. The study reshapes the universal family tree, adding ...

Viruses: More survival tricks than previously thought

March 5, 2013

Among eukaryotes with modified nuclear genetic codes, viruses are unknown. Until now it had been believed that the modifications to the genetic code effectively prevented new viral infections. However, researchers have now ...

Recommended for you

Understanding how to control 'jumping' genes

June 22, 2018

A team of Texas A&M University and Texas AgriLife Research scientists have made a new discovery of how a single protein, Serrate, plays dual roles in controlling jumping genes.


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 14, 2013
"This research appeared on the front page of Science on July 19, 2013."

1 / 5 (2) Oct 14, 2013
"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."

No it doesn't.
not rated yet Oct 16, 2013
@seanclin: Well, in the sense of the suggested phylogeny of those papers it (arguably) does. Maybe someone will come up with better models.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.