Scientists have discovered the fingerprints of mysterious viruses that were hiding in an ancient group of microbes.
This week in the journal Nature Microbiologythree papers devoted to viruses of the archaea of the Asgard group were published at once. Scientists have examined the genomes of viruses from genomic and metagenomic data and studied their relationship with the most famous groups of viruses. The data obtained helped scientists to guess what exactly were the functions of the viruses that infected the Asgard archaea.
Notably, this is the first studyarchaeal Asgard viruses; nothing was known before. In the future, this line of research may show whether and how viruses were involved in the emergence of eukaryotic cells on Earth.
In general, the archaea of the Asgard group have many geneswhich encode eukaryotic proteins. Scientists also consider them to be the closest relatives of eukaryotes. However, until now, researchers did not know whether the similarities between members of the Asgard group and eukaryotes extended to the viruses that infect them.
The first group of scientists analyzedmetagenomic sequences. They were obtained from deep-sea hydrothermal deposits. Biologists have collected six genomes of viruses that infect the archaea of the Asgard group. It turned out that they belong to four viruses, they were called Fenrir (Fenrir), Sköll (Skoll), Nidhogg (Nidhogg) and Ratatoskr (Ratatoskr). All of them are creatures from Scandinavian mythology.
Based on genomic data, biologistssuggested that they are capable of semi-autonomous genome replication, repair, epigenetic modification, and transcriptional regulation. They also combine features of bacterial and archaeal viruses.
Another group of scientists has obtained the complete genome of an archaeafrom the Asgard group and reassembled the genome of strain LCB_4, which was considered a basal group of the phylum Odinarchaeota. Biologists have discovered the sequences of two viruses, they were named Huginn and Muninn (Hugin and Munin are a pair of ravens in Scandinavian mythology that fly around the world of Midgard and report to the god Odin about what is happening). Viruses related to them were found in the genomes of other prokaryotes, including the archaea of the Asgard group.
The third work is devoted to metagenomic assembly 20new archaeal viruses of the Asgard group from sediment samples. By combining phylogenetic analysis with searches for CRISPR loci in metagenomic data, the researchers divided the viruses found into three family-level groups.
Ultimately, the researchers were able to figure out the functions of only some of the virus genes. The functions of the vast majority of genes are still unknown.
Asgard or Asgardarchaeota - presumeda superphylum consisting of a group of archaea that includes Lokiarchaeota, Thorarchaeota, Odinarchaeota and Heimdallarchaeota. It appears that eukaryotes originated within Asgard, in the branch containing the Heimdallarchaeota. This means that archaea from the Asgard group, many biologists suggest, are closest to the ancestors of all organisms that have cell nuclei. They could have contributed to the emergence of complex life
The research results can be found here, here and here.
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