In “Megavirus May Be Stripped-Down Version of Normal Cell” (Wired,
October 11, 2011), John Timmer/Ars Technica discusses the view that the recently discovered megavirus is a former cell:
Giant viruses, its authors argue, have all these genes normally associated with cells because, in their distant evolutionary past, they were once cells.
Mimivirus was discovered in an amoeba, so the authors of the new paper used a simple technique to look for its relatives: take three different species of amoeba, expose them to a variety of environmental samples, and see if anything big starts growing in them. They hit pay dirt with a sample obtained from an ocean monitoring station just off the coast of Chile. Despite the oceanic source, the virus grew nicely in fresh water amoebae. The site also gave the virus its name: Megavirus chilensis.
The authors followed its lifestyle, showing that it behaved much like Mimivirus, forming similar structures within its host cell that could only be distinguished using electron microscopy. They also sequenced its entire genome, which turned out to be the largest virus genome yet completed: 1.26 million base pairs of DNA (Megabases).
For decades, viruses were not regarded as a form of life, but that may need revisiting.