A team of scientists at the University of Innsbruck has discovered over 30,000 viruses hidden in the DNA of unicellular organisms. This was possible through sophisticated detective work and the high-performance computer cluster, “Leo.” The viruses, which are not harmful to their hosts, and some may even protect them, are built into the genome of the microbes. Sometimes, up to 10% of microbial DNA consists of these built-in viruses. The study published in Proceedings of the National Academy of Sciences also found that many of the Earth’s abundant single-celled eukaryotic (complex) organisms are packed with viruses.
It is not yet clear why so many viruses are found in the genomes of microbes. However, the researchers believe that the built-in viruses protect the cell from infection by dangerous viruses. Many eukaryotic single-celled organisms are infected by “giant viruses,” which can be as large as bacteria. These infections kill the host by creating new copies of the giant virus. However, when a virophage, a virus that infects and destroys other harmful viruses, resides in the host cell, it can ‘reprogram’ 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 research project was based on a new group of viruses discovered in the water of the Gossenköllesee in Tyrol, Austria, in 2021. The researchers wanted to find the origin of these viruses, but they did not know which organisms they usually infected. Therefore, they conducted a large-scale study to test all microbes whose DNA sequences are known. The sequences of viruses, which could only be found thanks to state-of-the-art technology, were similar to virophage DNA. The host microbes probably protect themselves from giant viruses through these built-in viruses.
This unexpected discovery will inspire more research to study these viruses’ roles and determine why they are found in the genomes of microbes. The researchers hope to gain a deeper understanding of how viruses interact with their hosts and how they contribute to the diversity of life on Earth.
References
- Bellas, C., Hackl, T., Plakolb, M.-S., Koslová, A., Fischer, M. G., & Sommaruga, R. (2023). Large-scale invasion of unicellular eukaryotic genomes by integrating DNA viruses. Proceedings of the National Academy of Sciences, 120(16), e2300465120. https://doi.org/10.1073/pnas.2300465120
- University of Innsbruck. (2023, April 11). Stowaways in the Genome. University of Innsbruck Newsroom; University of Innsbruck. https://www.uibk.ac.at/en/newsroom/2023/stowaways-in-the-genome/
