Scientists have identified an enigmatic virus whose genome appears to be almost entirely new to science, populated by unknown genes that have never been documented in viral research. The so-called Yaravirus, from the name of Yara - or Iara, a figure of water queen in Brazilian mythology - was recovered from the Pampulha lake, an artificial lake in the Brazilian city of Belo Horizonte. While Yaravirus (Yaravirus brasiliensis) may not be a supernatural siren, the virus may prove to be as mysterious as the legend's aquatic nymph. This is because the virus constitutes "a new lineage of amoebic virus with puzzling origin and phylogeny," explains the research team in a new pre-printed document on the discovery. Two of the older members of that team - virologists Bernard La Scola from the University of Aix-Marseille in France and Jônatas S. Abrahão from the Federal University of Minas Gerais in Brazil - should know what they are talking about. Two years ago, the couple helped discover another viral novelty that resides in water: tupanvirus, a giant virus found in extreme aquatic habitats. Giant viruses, unlike the regular variety, are so called because of their huge capsid (protein shells that encapsulate virions - viral particles). These much larger viral forms were only discovered in this century, but they are not only remarkable for their size. They also possess more complex genomes, giving them the ability to synthesize proteins and therefore perform things like DNA repair, as well as DNA replication, transcription and translation.
Before their discovery, it was thought that viruses could not do such things, being considered non-inert and non-living entities, capable only of infecting their hosts. We now know that viruses are much more complex than previously believed, and in recent years scientists have discovered other types of viral forms that likewise challenge our thinking about how viruses can spread and function. The new discovery, Yaravirus, does not appear to be a giant virus, composed as it is of small 80 nm particles. But what is noteworthy is how apparently unique its genome is. "Most of the known amoeba viruses have been seen to share many features that ultimately prompted authors to classify them into common evolutionary groups," the authors write. "Contrary to what is observed in other isolated amoeba viruses, Yaravirus is not represented by a large / giant particle and a complex genome, but at the same time it carries an important number of genes not previously described." In their research, the researchers found that over 90 percent of the Yaravirus genes had never been described before, making up what are known as orphan genes (aka ORFans). Only six genes found had a distant resemblance to known viral genes documented in public scientific databases and a search through over 8,500 publicly available metagenomes offered no clue as to what Yaravirus could be closely related to. "Using standard protocols, our very first genetic analysis was unable to find recognizable capsid sequences or other classic viral genes in Yaravirus," the researchers explain. "Following current metagenomic protocols for viral detection, Yaravirus would not even be recognized as a viral agent."
As for what Yaravirus really is, scientists can only speculate for now, but suggest that it may be the first isolated case of an unknown group of amebal viruses, or potentially a distant type of giant virus that somehow may have evolved. in a reduced form. However, it is clear that we still have a lot to learn, researchers say. "The amount of unknown proteins that make up Yaravirus particles reflects the variability that exists in the viral world and how much potential of the new viral genome has yet to be discovered," the authors conclude.
The findings are reported in bioRxiv.