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Giant Viruses Gobbled Genes

At some points in their evolution, giant viruses amassed new genes, while losing them at others, Ars Technica reports. They are also unlikely to have been involved in the origin of cells, it adds.

Researchers from the US and Austria uncovered a group of giant viruses, dubbed Klosneuviruses, from metagenomic data generated from samples collected at a wastewater treatment plant. As they report in Science, researchers led by the Joint Genome Institute's Tanja Woyke found that one Klosneuvirus genome was some 1.57 megabases large.

In addition, Woyke and her colleagues noted that these viruses appeared rather cell-like. For instance, they encoded an expanded set of translational machinery that would enable them to generate all 20 amino acids. Through a phylogenetic analysis, the researchers found that Klosneuviruses didn't, though, evolve from ancient cells, but evolved from smaller viruses that took up host genes over time, while also losing genes.

The researchers proposed what they call an "accordion model" for their evolution, Ars Technica adds. "Under some circumstances, the virus goes through periods where it loses genes, slimming down in size somewhat," it says. "In other times, the virus picks up new genes, with a preference for certain functions."

However, Aix-Marseille University's Jean-Michel Claverie, one of the discoverers of giant viruses, points out to Science in a related news piece that the researchers haven't yet isolated the viruses, just their genetic material. "I am waiting to see a real virus isolated with its host in a [test] tube before I would believe any of their evolutionary interpretation," he says.