Biggest giant virus: Carries 2,300 genes

In today's issue of the journal *Science*, researchers report the discovery of a giant virus larger than the previously known largest Megavirus. These viruses are so large that they can be seen directly under a conventional optical microscope. The researchers have named them Pandoraviruses.

The researchers describe finding two new viruses, Pandoravirus salinus and Pandoravirus dulcis, in the Tunquen River estuary in Chile and in a freshwater pond near Melbourne, Australia, respectively. These viruses are larger than many parasitic bacteria, with the largest one containing 2.8 million base pairs and approximately 2,500 potential genes, while a common bacterium like *E. coli* has 4.6 million base pairs.

After conducting a series of analyses, the researchers stated that the origin of these giant viruses cannot be traced back to any currently known viral lineages.