An article published in the journal “Science” describes the identification of a new group of giant viruses that were called Klosneuviruses. A team of researchers at the U.S. Department of Energy Joint Genome Institute (DOE JGI) and the University of Vienna believe that they evolved from normal-sized viruses acquiring genes from their host organisms growing abnormally for viruses.
Giant viruses were discovered in 2003 and the first ones were called Mimiviruses. Over the following years others really huge for virus standards were discovered: the Pandoraviruses have a size of a micrometer and the species Pandoravirus salinus has about 2,500 genes, really a lot if you think that the influenza virus has only 13 genes.
In many ways these giant viruses seem more like bacteria and these strange features sparked discussions about their origin. The opinions among biologists about viruses in general are already very different, about the origin of giant viruses so far there are two main hypotheses: that they’re the last survivors of a type of extinct ancestral cells or that they’re an evolution of normal-sized viruses. According to the discoverers of the Klosneuviruses the second hypothesis is the correct one.
The Klosneuviruses were discovered in a waste water treatment plant in the town of Klosterneuburg, Austria. These giant viruses have about 700 genes in common with eukaryotic cells belonging to different phyla and that makes it impossible to be inherited through common mechanisms. The researchers claim that the only explanation is that those are genes acquired over time from a series of infected organisms.
Another conclusion reached by the analysis of the Klosneuviruses is that they belong to the same group as the Mimiviruses. For this reason they were included in their family, called Mimiviridae, where in the past another species of giant virus called Cafeteria roenbergensis virus – after the name of the creature they use as a host – was also included.
Professor Jean-Michel Claverie, among the discoverers of Mimiviruses, Megaviruses and Pandoraviruses, is skeptical about these discoveries. For years, he’s been argueing that giant viruses are the last survivors of a type of cells that belong to a different domain of living beings.
According to Jean-Michel Claverie the genetic analysis of the Klosneuviruses produced “chimeric” genomes mixing the virus ones with those of other organisms mixed together in the samples. In essence, it’s a contamination problem that affected the genetic analysis, an ever-present risk in these cases and the reason why a great attention needs to be payed during this type of operation.
A proof acceptable to Jean-Michel Claverie would be an analysis carried out on a Klosneuvirus isolated with its host organism. At this point, further studies seems inevitable to check if the results of this research are correct and assess with greater certainty the nature of the Klosneuviruses.