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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