Huge viruses may represent new life form

Two newly discovered giant viruses - more than twice as big as the last largest known viruses - unearthed in Chile and Australia, may represent a completely new life form, a new study suggests.
Even more gigantic viruses might await discovery and they may have features that could blur the lines between life and viruses, which are not considered to be living things, French scientists said.
Ten years ago, a team of researchers had discovered mimivirus, what until now was the biggest, most complex virus known. Mimivirus and its relatives, the megaviruses, can reach sizes of more than 700 nanometres and possess more than 1,000 genes, features typical of parasitic bacteria.

The same team has now discovered the new record-breaking viruses which are visible with a traditional light microscope, being a full micrometre or millionth of a metre in size.
They also each possess a whopping roughly 2,500 genes, way more than many viruses, such as influenza or HIV, which get along very well with 10 or fewer genes.
More than 93 per cent of their genes resemble nothing known and analysis of their genomes suggests they are not related to any known virus family.

The shape of these new viruses, which resemble ancient Greek jars, reminded the scientists of the myth of Pandora's box, giving the germs their name - pandoraviruses.

"The opening of the box will definitively break the foundations of what we thought viruses were," researcher Chantal Abergel, research director at the French National Center for Scientific Research in Marseille, told LiveScience.
The researchers found pandoraviruses by looking at amoebas. One virus, named Pandoravirus salinus, was unearthed at the mouth of the Tunquen River off the coast of central Chile, while the other, called Pandoravirus dulcis, was found at the bottom of a shallow freshwater pond near Melbourne.
It is a mystery why pandoraviruses have more than 2,500 genes while most viruses have far less, researchers said.
According to one controversial suggestion, giant viruses and other viruses that depend on DNA as their genetic material may be the shrunken descendants of living, cellular ancestors.

"Parasites of any kind are submitted to the universal process of 'genome reduction' - that is, they may lose genes without harm, because the host can always provide the missing function," said Jean-Michel Claverie, head of the Structural and Genomic Information Laboratory in Marseille, France.
DNA viruses small and giant may all have degenerated from the same or similar cellular ancestors, "but only differ by the rate by which they lost genes from the starting ancestral genome," Claverie said.
Future research could turn up "even more intermediary life forms between viruses and cells, establishing a continuity between the two," Abergel said.