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New giant viruses in some sewage treatment plants discovered by researchers
Viruses are distributed worldwide in a huge variety. Scientists believe that more viruses live on our planet than there are stars in the Milky Way. It has only been known for a relatively short time that viruses also contain excessive large species. Several previously unknown giant viruses have now been discovered in samples from sewage treatment plants. The viruses from the group of Klosneuviren 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 just as big as bacteria, their genome is also made of DNA and is comparably extensive, reports the research team around 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 sewage treatment plant Klosterneuburg. With the results of the investigation, an important step has been taken in understanding the evolution of viruses, the researchers report. The results of their study have been published in the journal "Science".
In sewage sludge samples from Klosterneuburg, scientists have discovered a previously unknown genus of giant viruses. (Image: stu12 / fotolia.com) Search for bacteria leads to the discovery of giant viruses
In fact, the scientists studied certain bacteria that play an important role in the Earth's natural nitrogen cycle. In samples from the sewage treatment plant Klosterneuburg 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," says first author Frederik Schulz, who was still a doctoral student at the University of Vienna at the time of the study. In fact, giant viruses have only been known for about ten years and were originally discovered in simple amoebas in southern France, explains Matthias Horn, doctoral supervisor of Frederik Schulz. Science now assumes that these viruses are widespread.
Viruses with gigantic extensive genetic material
The now discovered Klosneuviren have, according to the researchers, a "gigantically extensive genome for viruses." In addition, no other previously known virus similar genes have been discovered for protein biosynthesis. As typical of giant viruses, the researchers also describe the lack of similarities with other viruses or organisms in much of their genome. This fact also raises some questions. For example, whether the giant viruses are relics of their own life form, which originally emerged independently of microorganisms (bacteria and archaea) and the eukaryotes (such as plants and animals).
Better understanding of the evolution of viruses
With the discovery of the clovenneuviruses a better understanding of the evolutionary history of these viruses is possible, ending the years-long debate on the origin of giant viruses, the researchers report. The reconstruction of the evolutionary history of the clovenneuviruses has shown that the genome of the giant viruses was originally rather small - like that of other viruses. In the course of their evolution, the gigantic genomes of today's representatives were created by the incorporation of additional genes. These include the genes for protein biosynthesis, the scientists report. The latter are not derived from a previously unknown form of life, but are surprisingly similar to the genes of today's living things.
Specializing in collecting genes
"Giant viruses are therefore not relics of a fourth domain of life, but a highly unusual group of viruses that have specialized in the collection of genes of other organisms," emphasizes the study director at the Joint Genome Institute, Tanja Woyke. In order to better understand this unusual collecting passion of the viruses, now further investigations of Klosneuviren in the laboratory are required.
So far, however, it has not been able to isolate the virus particles. "We are currently trying to extract the viruses from new samples from Klosterneuburg by offering them single-celled amoebas for their own reproduction," explain Horn and Wagner.
Viruses with the properties of real life forms
For giant viruses are - as all known viruses - reliant on the cells of other organisms for propagation, even if they have properties that were previously known only from real life forms, such as the variety of building blocks for the production of proteins, report the Scientist. According to the researchers, the discovery of Klosneuviren is "a prime example of how scientific curiosity leads to completely unexpected discoveries that - in this case - concern fundamental questions of life." (Fp)