Up until recently, the line between viruses and cells seemed pretty simple: cells were big and carried everything they needed to live and grow. Viruses were tiny and only carried the genes they needed to take over their host cells; they relied on their hosts for most essential proteins.
That line got a bit blurry as we found parasitic and symbiotic cells with very stripped-down, minimalist genomes that wouldn’t let them survive outside their hosts. But it’s nearly been obliterated by the discovery of giant viruses—some of these have genomes that are larger than those of bacteria and carry many of the genes needed to copy DNA and translate it into proteins.
Scientists have now identified yet another giant virus, this time using a technique that sounds like it’s straight out of a sci-fi horror flick: they thawed some 30,000-year-old permafrost and allowed any viruses present to infect some cells. Fortunately, the cells were amoebas, and this virus is overwhelmingly unlikely to present a threat to human health. But the fact that viruses could apparently survive so many centuries in the Siberian permafrost does lead the authors to suggest that the melting Arctic may pose an emerging disease risk.
The authors of the new paper, a mix of French and Russian researchers, identified the virus using a procedure that’s incredibly simple: take a culture of amoebas (a strain that has been found in the permafrost) and put a bit of permafrost in with the culture. After that, it was a matter of waiting for something bad to happen to the amoebas.
Largest viral genome yet carries 2,300 genes that are new to biology | The enormous new virus is visible with a light microscope.
The something bad in this case happened to be the explosion, or lysis, of the cells. A check of the culture showed the presence of a giant virus particle, shaped similarly to the Pandoravirus described in the article linked above. In terms of the sheer physical size of the virus, it’s the largest one we’ve yet discovered. Because of its jug-like shape, the authors named it Pithovirus after a type of amphora used by Pandora (the namesake of the second largest virus).