Microorganisms reveal how our single-celled predecessors incorporated viral DNA into their own genomes.
Researchers have discovered remnants of ancient giant viruses in the genome of Amoebidium, a single-celled organism, suggesting that such viral sequences may have played a role in the evolution of complex life forms. This study highlights the dynamic relationship between viruses and their hosts, also reflecting on human genetics.
A surprising twist in the evolutionary history of complex life has been uncovered in a new study published in Science Advances. Researchers at Queen Mary University of London have found that a single-celled organism, closely related to animals, contains remnants of ancient giant viruses within its genetic code. This discovery provides insight into how complex organisms may have acquired some of their genes and underscores the dynamic interplay between viruses and their hosts.
The study focused on a microbe called Amoebidium, a unicellular parasite found in freshwater environments. By analyzing Amoebidium’s genome, the researchers led by Dr. Alex de Mendoza Soler, Senior Lecturer at Queen Mary’s School of Biological and Behavioural Sciences, found a surprising abundance of genetic material originating from giant viruses – some of the largest viruses known to science. These viral sequences were heavily methylated, a chemical tag that often silences genes.
“It’s like finding Trojan horses hiding inside the Amoebidium’s DNA,” explains Dr de Mendoza Soler. “These viral insertions are potentially harmful, but Amoebidium seems to be keeping them in check by chemically silencing them.”
The microbe Amoebidium appalachense undergoing its developmental life cycle in the laboratory. The nuclei divide within a cell until maturity (~40h in the video), when each nucleus becomes a single cell and the colony breaks giving rise to the progeny. Credit: Alex de Mendoza
Ongoing Research and Implications
The researchers then investigated how widespread this phenomenon might be. They compared the genomes of several Amoebidium isolates and found significant variation in the viral content. This suggests that the process of viral integration and silencing is ongoing and dynamic.
“These findings challenge our understanding of the relationship between viruses and their hosts,” says Dr. de Mendoza Soler. “Traditionally, viruses are seen as invaders, but this study suggests a more complex story. Viral insertions may have played a role in the evolution of complex organisms by providing them with new genes. And this is allowed by the chemical taming of these intruders’ DNA.”
Furthermore, the findings in Amoebidium offer intriguing parallels to how our own genomes interact with viruses. Similar to Amoebidium, humans and other mammals have remnants of ancient viruses, called Endogenous Retroviruses, integrated into their DNA. While these remnants were previously thought to be inactive “junk DNA,” some might now be beneficial. However, unlike the giant viruses found in Amoebidium, Endogenous Retroviruses are much smaller, and the human genome is significantly larger. Future research can explore these similarities and differences to understand the complex interplay between viruses and complex life forms.
Reference: “DNA methylation enables recurrent endogenization of giant viruses in an animal relative” by Luke A. Sarre, Iana V. Kim, Vladimir Ovchinnikov, Marine Olivetta, Hiroshi Suga, Omaya Dudin, Arnau Sebé-Pedrós and Alex de Mendoza, 12 July 2024, Science Advances.
DOI: 10.1126/sciadv.ado6406
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