Scientists have discovered a new virus in Brazil, the DNA of which is 90 percent of genes unknown to science. The results of the discovery are published on the bioRxiv preprint site.
The virus was detected in the artificial lake Pampulha in the Brazilian city of Belo Horizonte. Its not very complex genome consists almost entirely of genes unknown to science. The authors named the new virus Yaravirus brasiliensis after the water nymph Yara from the mythology of the peoples of South America.
Scientists speculate that they are faced with the first case of an unknown isolated group of viruses or a distant species of a giant virus that has evolved into a smaller form.
Discovered only in the 21st century, giant viruses reach sizes comparable to those of a bacterial cell. They got their name because of their huge capsids - protein membranes that encapsulate virions - viral particles. They also have DNA of the appropriate length, which exceeds 200 thousand base pairs and often contains the so-called orphan, or orphan genes (ORFan), which are not found in any other group of organisms.
Complex genomes enable giant viruses to synthesize proteins and therefore perform DNA repair, replication, transcription, and translation. Before their discovery, it was believed that viruses do not have such abilities, since they are inert creatures that can only infect their hosts. All known giant viruses are parasites of amoebas.
And although the size of the new microorganism is significantly smaller than that of giant viruses - about 80 nanometers - it also parasitizes on amoebas, and its genome is almost completely orphan: 68 of its genes (more than 90 percent) do not find analogues in any known organism, and only six vaguely similar to those known to science.
“This is because the virus is a new lineage of amoebic virus with amazing origins and phylogeny,” one of the study leaders, Jônatas Abrahão of the Federal University of Minas Gerais in Brazil, said in a press release.
Scientists have analyzed more than eight and a half thousand metagenomes, but have not found among them viruses related to the new microorganism. Like other viruses of this group, it is represented by double-stranded DNA, the length of which is 44,900 base pairs and contains 74 coding fragments.
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“Using standard protocols, our very first genetic analysis failed to detect any recognizable capsid sequences or other classic viral genes in the yaravirus,” explains Yonatas Abrajao and second study leader Bernard La Scola of Aix-Marseille University in France.
According to the official metagenomic protocols, yaravirus cannot even be recognized as a viral agent, because it has no clear similarity with them. Scientists cannot yet say what he really is - a representative of a completely new group or a descendant of a giant virus that somehow evolved into a smaller form.
“The number of unknown proteins that make up the particles of the yaravirus reflects the variability that exists in the viral world and how many new viral genomes have yet to be discovered,” the authors conclude.
