MSGID: 1:317/3 643633e2   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Stowaways in the genome    
    Thousands of unknown viruses hide in the DNA of unicellular organisms   
      
      
     Date:   
         April 11, 2023   
     Source:   
         University of Innsbruck   
     Summary:   
         Scientists have discovered over 30,000 viruses by using the high-   
         performance computer cluster 'Leo' and sophisticated detective   
         work. The viruses hide in the DNA of unicellular organisms. In   
         some cases, up to 10% of microbial DNA consists of built-in viruses.   
      
      
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   FULL STORY   
   ==========================================================================   
   At the University of Innsbruck, scientists have discovered over   
   30,000 viruses by using the high-performance computer cluster "Leo" and   
   sophisticated detective work. The viruses hide in the DNA of unicellular   
   organisms. In some cases, up to 10% of microbial DNA consists of built-in   
   viruses.   
      
      
   ==========================================================================   
   During a large-scale study of complex single-celled microbes,   
   Dr. Christopher Bellas, Marie-Sophie Plakolb and Prof. Ruben Sommaruga   
   from the Department of Ecology at the University of Innsbruck made an   
   unexpected discovery. Built into the genome of the microbes, they found   
   the DNA of over 30,000 previously unknown viruses. This "hidden" DNA may   
   allow the replication of complete and functional viruses in the host cell.   
      
   "We were very surprised by how many viruses we found through this   
   analysis," says Bellas. "In some cases, up to 10% of a microbe's DNA   
   turned out to consist of hidden viruses." These viruses do not appear   
   to harm their hosts. On the contrary, some may even protect them. Many   
   appear to be similar to so-called virophages. These viruses infect and   
   destroy other, harmful viruses that infect their host cell.   
      
   The study, financed by the Austrian Science Fund (FWF), was published   
   in the journal Proceedings of the National Academy of Sciences (PNAS)   
   and was carried out in collaboration with researchers from the Max Planck   
   Institute for Medical Research and the University of Groningen.   
      
   Viruses as protectors From bacteria to humans, all life forms are   
   continuously infected with viruses.   
      
   Some are constantly present, but only occasionally trigger symptoms,   
   such as the herpes virus in humans. Others hide even deeper, becoming   
   part of their host's DNA. This study found that many of the Earth's   
   abundant single-celled eukaryotic (complex) organisms are packed with   
   viruses. These organisms are found everywhere, and include abundant   
   algae in lakes and oceans, amoebae in soil, as well as human parasites.   
      
   "Why so many viruses are found in the genomes of microbes is not yet   
   clear," says Bellas. "Our strongest hypothesis is that they protect the   
   cell from infection by dangerous viruses." Many eukaryotic single-celled   
   organisms are infected by "giant viruses," a group of viruses that can be   
   as large as bacteria. These infections kill the host as they create new   
   copies of the giant virus. However, when a virophage resides in the host   
   cell, it 'reprograms' the giant virus to build virophages. As a result,   
   the giant virus can sometimes be fended off and the host cell population   
   is saved from destruction.   
      
   The DNA of the newly discovered viruses is similar to virophage   
   DNA. Therefore, it is probable that the host microbes protect themselves   
   from giant viruses through these built-in viruses.   
      
   DNA from an alpine lake The research project was originally based on a   
   new group of viruses that Bellas and Sommaruga discovered in the water   
   of the Gossenko"llesee in Tyrol, Austria, in 2021. "Initially, we wanted   
   to find the origin of the new 'Polinton-like viruses' with our study,"   
   explains Bellas. "However, we did not know which organisms are usually   
   infected by these viruses. That's why we conducted a large-scale study   
   to test all microbes whose DNA sequences are known."  The huge data   
   set which the researchers examined only contains DNA sequences, i.e. a   
   sequence of the letters ATGC from which all genes are encoded.   
      
   Nevertheless, the data set consists of several hundred gigabytes.   
      
   The sequences of viruses, tiny by comparison, could only be found in   
   this large amount of data thanks to state-of-the-art technology. With the   
   high-performance computer cluster "Leo" of the University of Innsbruck,   
   the data set could be analysed quickly. DNA sequences from microbes were   
   also read using the new Oxford Nanopore technology. With this technology,   
   DNA is passed through tiny pores in a membrane. Each base -- A, G,   
   C or T -- interrupts an electric current and thus generates a signal   
   from which the DNA sequence can be read.   
      
   In the end, the researchers found much more than the viruses they were   
   looking for. This unexpected discovery will inspire more research to   
   study the roles that these viruses play.   
      
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Microbes_and_More # Virology # New_Species #   
                   Biochemistry_Research # Biology # Microbiology #   
                   Biotechnology # Soil_Types   
       * RELATED_TERMS   
             o Virus o DNA o DNA_microarray o Avian_flu o Mutation o   
             Microorganism o Gene_therapy o Prokaryote   
      
   ==========================================================================   
   Story Source: Materials provided by University_of_Innsbruck. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Christopher Bellas, Thomas Hackl, Marie-Sophie Plakolb, Anna   
      Koslova',   
         Matthias G. Fischer, Ruben Sommaruga. Large-scale invasion   
         of unicellular eukaryotic genomes by integrating DNA   
         viruses. Proceedings of the National Academy of Sciences, 2023;   
         120 (16) DOI: 10.1073/pnas.2300465120   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/04/230411105915.htm   
      
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