Since the appearance of COVID-19, viruses have gotten a very bad name in the general public. These tiny intracellular parasites of living organisms are the most numerous biological entities on Earth and cause disease in humans, livestock and crops. Along with model bacterial viruses (phages), they have been studied in detail.
But not all of them are harmful; the vast majority of viruses do not harm us and infect bacterial cells – some of them even live inside our bodies without us even being aware of it. Others can fight against more dangerous viruses.
Now, in a global first, Tel Aviv University (TAU) scientists have discovered about 100,000 new types of viruses previously unknown to science – even specifying which organisms they are likely to attack. These viruses were discovered in global environmental data from soil samples, oceans, lakes, and a variety of other ecosystems.
The researchers believe that their discovery may help in the development of anti-microbial drugs and in protecting against agriculturally harmful fungi and parasites.
What's the difference between DNA and RNA viruses?
Compared with DNA viruses, the diversity and role of RNA viruses in microbial ecosystems are poorly understood. Recently, however, metatranscriptome surveys (bulk RNA sequencing of entire microbial communities) uncovered massive amounts of previously undetected RNA viruses.
DNA viruses like the poxvirus are packaged with their polymerase machinery so they can replicate in the host cytoplasm directly. RNA viruses infect cells by injecting RNA into the cytoplasm of the host cells to transcribe and replicate viral proteins.
The study was led by doctoral student Uri Neri under the guidance of Prof. Uri Gophna of the Shmunis School of Biomedicine and Cancer Research at TAU’s Wise Faculty of Life Sciences. The research was conducted in collaboration with the US National Institutes of Health (NIH) and the Joint Genome Institute (JGI) in the Department of Energy and the Pasteur Institute in France.
The research was published in the prestigious journal Cell under the title “Expansion of the Global RNA Virome Reveals Diverse Clades of Bacteriophages” and comprised data collected by more than 100 scientists around the world.
Viruses are genetic parasites, meaning they must infect a living cell to replicate their genetic information, produce new viruses and complete their infection cycle.
According to Neri, the study used new computational technologies to mine genetic information collected from thousands of different sampling points around the world – in oceans, soil, sewage, geysers and more. The researchers developed a sophisticated computational tool that distinguishes between the genetic material of RNA viruses and that of the hosts and used it to analyze the big data. The discovery allowed the researchers to reconstruct how the viruses underwent diverse acclimation processes throughout their evolutionary development in order to adapt to different hosts.
The researchers were able to identify viruses suspected of infecting various pathogenic microorganisms, thus opening up the possibility of using viruses to control them.
“The system we developed makes it possible to perform in-depth evolutionary analyses and to understand how the various RNA viruses have developed throughout evolutionary history,” explained Gophna.
“One of the key questions in microbiology is how and why viruses transfer genes between them. We identified a number of cases in which such gene exchanges enabled viruses to infect new organisms."
Prof. Uri Gophna
"Furthermore, compared to DNA viruses, the diversity and roles of RNA viruses in microbial ecosystems are not well understood. In our study, we found that RNA viruses are not unusual in the evolutionary landscape and, in fact, that in some aspects they are not that different from DNA viruses. This opens the door for future research, and for a better understanding of how viruses can be harnessed for use in medicine and agriculture.”