A groundbreaking study published in Science Advances unveils a surprising aspect of the evolutionary history of complex life. Researchers at Queen Mary University of London have identified remnants of ancient giant viruses embedded within the genetic material of a single-celled organism closely related to animals.
This discovery illuminates the dynamic relationship between viruses and their hosts, and suggests that some complex organisms might have acquired genes from viruses.
The research centered on Amoebidium, a unicellular parasite found in freshwater environments. By examining Amoebidium‘s genome, the team led by Dr. Alex de Mendoza Soler, a Senior Lecturer at Queen Mary’s School of Biological and Behavioural Sciences, uncovered a significant presence of genetic material from giant viruses, which are among the largest viruses known.
These viral sequences within Amoebidium‘s DNA were heavily methylated, a chemical modification that typically silences genes. “It’s akin to finding Trojan horses hidden inside Amoebidium‘s genetic code,” Dr. de Mendoza Soler explains. “Although these viral insertions could be harmful, Amoebidium appears to manage them by chemically silencing them.”
The researchers extended their investigation to determine the prevalence of this phenomenon, comparing the genomes of several Amoebidium isolates. They discovered considerable variation in viral content, indicating that the integration and silencing of viral DNA is an ongoing and dynamic process.
“These discoveries challenge our conventional understanding of virus-host relationships,” states Dr. de Mendoza Soler. “Viruses are traditionally viewed as invaders, but this study suggests a more nuanced narrative. Viral insertions may have contributed to the evolution of complex organisms by introducing new genes, and this has been facilitated by the chemical suppression of these viral elements.”
The study’s findings regarding Amoebidium draw intriguing parallels to how human and other mammalian genomes interact with viruses. Similar to Amoebidium, humans have remnants of ancient viruses, known as Endogenous Retroviruses, incorporated into their DNA.
These remnants, once considered inactive “junk DNA,” may now be recognized as potentially beneficial. However, unlike the giant viruses in Amoebidium, Endogenous Retroviruses are much smaller, and the human genome is vastly larger. Future research can delve into these similarities and differences to further comprehend the complex interplay between viruses and complex life forms.
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