Researchers in Brazil have discovered an amoeba-infecting virus with a large amount of unknown genes. The team found that over 90 percent of the genes in the virus have not been found anywhere else in the world, suggesting that this organism may belong to a brand-new class of viruses that we did not know existed.
The discovery is reported in a paper published in the preprint server bioRxiv and is yet to be peer-reviewed. The organism is called Yaravirus, after Yara "the mother of waters” in Indigenous Tupi-Guarani mythology. The virus was discovered in Acanthamoeba castellanii, one of the best-known species of this protozoa. The sample was collected from the muddy waters of an artificial lake called Pampulha in the city of Belo Horizonte, Brazil.
The team compared the virus' 74 protein-encoding genes to a database containing over 8,500 metagenomes. Of the 74 genes, only six were distantly related to known genetic material from other microorganisms, making it difficult for researchers to work out where it came from and to what species it's related to.
“Yaravirus represents a new lineage of viruses isolated from A. castellanii cells. The amount of unknown proteins composing the Yaravirus particles reflects the variability existing in the viral world and how much potential of new viral genomes are still to be discovered,” note the researchers in the paper.
The finding is both exciting and perplexing for the authors. Viruses that infect amoebas tend to share a lot in common, with all known isolated amoebal viruses related to the so-called giant viruses (nucleocytoplasmic large DNA viruses, NCLDVs), which are much larger than typical viral agents and more complex. But Yaravirus is peculiar in this respect.
"Contrary to what is observed in other isolated viruses of amoeba, Yaravirus is not represented by a large/giant particle and a complex genome, but at the same time carries an important number of previously undescribed genes, including one encoding a novel major capsid protein," explained the authors.
It is unclear if this is the first example of a brand new family of amoebal viruses that evolved independently or if it used to be a giant virus that decreased in size over time, now reaching just 80 nanometers across (compared to giant viruses that can be between 200 and 400 nanometers across). For comparison, a red blood cell is 100 times bigger than the Yaravirus. If the Yaravirus is truly related to the giant viruses, it would be the smallest member of the NCLDVs, both in particle and genome size.
There is certainly more to come about this newly discovered virus and likely not just from amoebas.
[H/T: Science Magazine]