The concept of viruses in the giant viruses era

Orateur : Chantal ABERGEL (Information Génomique et Structurale, CNRS UMR7256, Marseille)

In the mind of most biologists, a “virus” remains the most reduced and optimized vehicle to propagate a nucleic acid molecule at the expense of a cellular host, an ultimate parasite at the frontier of the living world. With genome sizes and gene contents larger than many bacteria, as well as particle sizes of the order of half a micron the Megaviridae have clearly made the point that being small and simple should no longer be considered fundamental properties of viruses, nor a testimony of their evolutionary origin. More recently, the discovery of the Pandoraviruses, with amphora shaped virions over a micrometer in length and genome sizes up to 2.8 Mb, surpassing the complexity of the smallest eukaryotic cells, raised a number of fundamental questions about giant viruses’ origin and their mode of evolution. The convergence between the discovery of increasingly reduced parasitic cellular organisms and that of giant viruses exhibiting a widening array of cellular-like functions may ultimately abolish the historical discontinuity between the viral and the cellular world. We will finally discuss the biodiversity of giant DNA viruses in the light of recent discoveries.

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