Tree of Life
Image: Tree of Life Web Project
The current phylogenetic tree, which organizes the known types of life into groups that share certain characteristics, may have just gained an extra branch way down near the roots. There are three domains: Archaea, Bacteria, and Eukoryota.
While we are used to hearing about a new species of frog or beetle or plant being discovered, these are usually branches or even twigs far up the Eukaryotic line. And it’s accepted that only a fraction of bacteria, one of the three main branches, have been identified.
So it’s kind of major news that a family has been found that don’t fit anything yet known. French scientists at CNRS, the French national research agency, have found viruses that are massive (massive compared to other known viruses, that is). They are large enough to be seen with a regular light microscope, and have almost twice the number of genomes, a different structure and different physical appearances from that of other known viruses.
Pandoraviruses have a much bigger genome, an atypical shape, and different genes from megaviruses (inset), the next largest viruses known to date.
Credit: IGS – CNRS/AMU; IGS CNRS-AMU/Chantal Abergel Via Science
From the original paper: “Because more than 93% of Pandoraviruses genes resemble nothing known, their origin cannot be traced back to any known cellular lineage…The absence of Pandoravirus-like sequences from the rapidly growing environmental metagenomic databases suggests either that they are rare or that their ecological niche has never been prospected.”
I count it as a good day when a major assumption is expanded or upended by scientific research. I would welcome the Pandoravirus family to the Tree of Life, but congratulations are more appropriate in the other direction. Thank you, researchers, for alerting us to something that has been right under our collective noses.
More:
Science paper – Pandoraviruses: Amoeba Viruses with Genomes Up to 2.5 Mb Reaching That of Parasitic Eukaryotes by N. Philippe, M. Legendre, G. Doutre, Y. Couté, O. Poirot, M. Lescot, D. Arslan, V. Seltzer, L. Bertaux, C. Bruley, J. Garin, J-M. Claverie, C. Abergel
Science article – Ever-Bigger Viruses Shake Tree of Life by Elizabeth Pennisi