Researchers have found that a single-celled organism, a close relative of animals, contains traces of ancient giant viruses within its genetic material. This discovery provides insight into how complex organisms may have gained certain genes and emphasizes the dynamic relationship between viruses and their hosts.
A new study featured in Science Advances presents an unexpected twist in the evolutionary narrative of complex life. Scientists at Queen Mary University of London have uncovered that a single-celled organism, related to animals, retains fragments of ancient giant viruses incorporated into its genetic framework. This discovery clarifies how intricate organisms might have obtained specific genes and underscores the complex interactions between viruses and their hosts.
The research concentrated on a microbe known as Amoebidium, a unicellular parasite typically found in freshwater ecosystems. By examining the genome of Amoebidium, the team led by Dr. Alex de Mendoza Soler, Senior Lecturer at the School of Biological and Behavioural Sciences at Queen Mary, identified a surprising quantity of genetic material derived from giant viruses — among the largest viruses known to science. These viral sequences were notably methylated, a chemical label that can inhibit gene expression.
“It’s akin to discovering Trojan horses concealed within the DNA of Amoebidium,” explains Dr. de Mendoza Soler. “While these viral insertions could pose risks, Amoebidium appears to be managing them by chemically silencing their activity.”
Next, the researchers examined how common this phenomenon might be. They compared the genomes from different isolates of Amoebidium and noted considerable differences in viral content. This indicates that the process of viral integration and suppression is both active and evolving.
“These results challenge our traditional views on the virus-host relationship,” asserts Dr. de Mendoza Soler. “Typically, viruses are viewed as attackers, but this research suggests a more intricate narrative. Viral insertions could have contributed to the evolution of complex organisms by supplying new genes, facilitated by the chemical regulation of these foreign DNA fragments.”
Additionally, the discoveries regarding Amoebidium draw intriguing parallels to the way our own genomes interact with viruses. Much like Amoebidium, humans and other mammals host remnants of ancient viruses, referred to as Endogenous Retroviruses, integrated into their DNA. While these remnants were once dismissed as inactive “junk DNA,” some may have beneficial roles. However, in contrast to the giant viruses present in Amoebidium, Endogenous Retroviruses are considerably smaller, and the human genome is much larger. Future studies can delve into these similarities and differences to better understand the complex interactions between viruses and advanced life forms.
