Raoult later co-authored a paper in Nature Microbiology that challenged the cell-based definition of life and proposed redefining viruses as "capsid-encoding organisms."
Claverie also put forth a new way of interpreting viruses: They are a "transitory cell into the cell, hence more like regular living organisms," he said.
"Virologists focused too much on viruses as 'particles,' where I proposed that they should be considered an intermediary stage [to cellular life]—the same role spores or seeds play for plants, for instance," he said.
Research by Claverie and his colleagues further suggests that giant viruses may predate the emergence of living organisms with a nucleus, or eukaryotes.
(Related: "Weird Australia Rocks Are Earliest Signs of Life, Study Says" [June 7, 2006].)
"In fact, there are many arguments that suggest that these giant viruses may be the ancestor of the modern cell nucleus," the French scientist added.
The virophage Sputnik apparently harms the newly described mamavirus as it exploits its reproductive mechanism, bolstering the notion that giant viruses are on par with recognized life-forms as hosts for viruses and should be reclassified.
Raoult notes, however, that such ideas might not be met with universal approval.
"People can hate when you try to change very basic definitions," he said.
Eddie Holmes of the Center for Infectious Disease Dynamics at Pennsylvania State University said that it has long been known that viruses can infect other viruses.
"The difference here is that Sputnik is supposedly 'bad' for [the mamavirus]," Holmes wrote in an email. "However, I think this aspect of the study is rather tentative and needs more work."
Holmes added that he thinks "the debate over whether viruses are 'alive' is an entirely pointless one and of no scientific importance. It all depends on how you define life."
Eugene Koonin, a co-author of the new study at the National Institutes of Health in Bethesda, Maryland, echoed Holmes's comments that the question of whether viruses are living creatures is a nonissue.
"Is not a scientific question or, in any case, a question of any interest to scientists," Koonin stated.
"Viruses are certainly biological entities, and this is enough."
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