New giant viruses discovered in some sewage treatment plants by researchers

Researchers find huge viruses in samples from sewage treatment plants
Viruses are very common worldwide. Scientists assume that there are more viruses on our planet than there are stars in the Milky Way. It has only been known for a relatively short time that excessive large species also occur among viruses. Scientists have now discovered several previously unknown giant viruses in samples from sewage treatment plants. The viruses from the Klosneuviren group are a hundred times larger than the flu virus, but harmless to humans, the scientists report.

Viruses are usually much smaller than bacteria. However, there are exceptions. The so-called giant viruses are not only as large as bacteria, their genome also consists of DNA and is comparatively extensive, reports the research team led by Michael Wagner, Holger Daims and Matthias Horn from the University of Vienna and the Joint Genome Institute (USA). Among other things, the scientists discovered such giant viruses in samples from the Klosterneuburg sewage treatment plant. The researchers report that the test results have been an important step in understanding the evolution of viruses. They published the results of their study in the scientific journal Science.

Searching for bacteria leads to the discovery of the giant virus
The scientists actually investigated certain bacteria that play an important role in the Earth's natural nitrogen cycle. In samples from the Klosterneuburg sewage treatment plant, they came across the genome of unusual giant viruses.

"It was immediately clear to us that we were on the trail of something completely new," emphasizes lead author Frederik Schulz, who was still a doctoral student at the University of Vienna at the time of the study. Giant viruses have actually only been known for about ten years and were originally discovered in simple amoebas in southern France, explains Matthias Horn, PhD supervisor of Frederik Schulz. Science is now assuming that these viruses are widespread.

Viruses with gigantic, extensive genetic material
According to the researchers, the newly discovered lavatory viruses have “a genetically extensive genetic material.” In addition, no other virus known to date has discovered a similar number of genes for protein biosynthesis. The researchers also describe the lack of similarities with other viruses or living organisms in a large part of their genome as typical for giant viruses. This fact also raises some questions. For example, whether the giant viruses are relics of their own way of life that originally developed independently of microorganisms (bacteria and archaea) and eukaryotes (such as plants and animals).

Better understanding of virus evolution
With the discovery of the Klosneuviren a better understanding of the evolutionary history of these viruses is possible, which ends the long debate over the origin of the giant viruses, the researchers report. The reconstruction of the evolutionary history of the Klosneuviren showed that the genome of the giant virus was originally rather small - like that of other viruses. In the course of their evolution, the giant genomes of today's representatives were created by the incorporation of additional genes. This also includes the genes for protein biosynthesis, the scientists report. The latter do not come from a previously unknown form of life, but are surprisingly similar to the genes of today's living things.

Specialized in collecting genes
"Giant viruses are not relics of a fourth domain of life, but a highly unusual group of viruses that specialize in collecting genes from other organisms," emphasizes the study director at the Joint Genome Institute, Tanja Woyke. In order to better understand this unusual passion for collecting viruses, further tests of the toilet neuros in the laboratory are now necessary.

So far, however, it has not been possible to isolate the virus particles. "We are currently trying to extract the viruses from new samples from Klosterneuburg by offering them unicellular amoebas for our own propagation," explain Horn and Wagner.

Viruses with the properties of real living things
Because the giant viruses, like all known viruses, rely on the cells of other organisms to reproduce, even if they have properties that were previously only known from real living things, such as the large number of building blocks for the production of proteins, they report Scientist. According to the researchers, the discovery of the toilet neuros is "a prime example of how scientific curiosity leads to completely unexpected discoveries, which - in this case - concern fundamental questions of life." (Fp)

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