A new study has found that the genetic code of the single-celled Amoebidium contains remnants of ancient giant viruses, offering insights into the genetic evolution of complex life. This finding reveals that these viral genes, although potentially harmful, are kept inactive by chemical processes in Amoebidium DNA, suggesting a more complex relationship between viruses and their hosts that may impact our understanding of genetic evolution in other organisms , including humans.
Microorganisms reveal how our single-celled ancestors incorporated viral DNA into their own genomes.
Researchers have found remnants of ancient giant viruses in the genome of Amoebidium, a single-celled organism, suggesting that similar 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, which also reflects human genetics.
A surprising twist in the evolutionary history of complex life was discovered in a new study published in Scientific progress. Researchers at Queen Mary University of London have discovered that a single-celled organism closely related to animals contains remnants of ancient giant viruses in its genetic code. This discovery provides insight into how complex organisms may have acquired some of their genes and highlights the dynamic interaction between viruses and their hosts.
The study focused on a microbe called Amoebidium, a single-celled parasite found in freshwater environments. Analyzing the genome of Amoebidium, researchers led by Dr Alex de Mendoza Soler, senior lecturer in Queen Mary’s School of Biological and Behavioral Sciences, found a surprising abundance of genetic material originating from giant viruses – some of the largest viruses known of science. These viral sequences are highly methylated, a chemical marker that often silences genes.
“It’s like finding Trojan horses hidden inside Amoebidium DNA” explains Dr. de Mendoza Soler. “These viral insertions are potentially harmful, but Amoebidium appears to keep them in check by chemically silencing them.”
The microbe Amoebidium appalachense goes through its life cycle of development in the laboratory. Nuclei divide within the cell until maturity (~40 hours in the video), when each nucleus becomes a single cell and the colony disintegrates, giving rise to progeny. Credit: Alex de Mendoza
Current 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 virus 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. “Viruses have traditionally been 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 enabled by the chemical taming of the DNA of these intruders.”
Amoebidium appalachense cells stained for DNA (in blue, showing the nucleus) and actin (in green), highlighting cell membranes at the cellularization stage of the colony. Credit: Alex de Mendoza
Additionally, the findings in Amoebidium offer intriguing parallels to how our own genomes interact with viruses. Like Amoebidium, humans and other mammals have remnants of ancient viruses called endogenous retroviruses integrated into their DNA. While these residues were previously thought of as inactive “junk DNA,” some may now be beneficial. However, unlike the giant viruses found in Amoebidium, endogenous retroviruses are much smaller and the human genome is considerably larger. Future research can explore these similarities and differences to understand the complex interaction between viruses and complex life forms.
Reference: “DNA Methylation Enables Repeated Endogenization of Giant Viruses in an Animal Relative” by Luke A. Saar, Yana V. Kim, Vladimir Ovchinnikov, Marin Oliveta, Hiroshi Suga, Omaya Dudin, Arnau Sebe-Pedros, and Alex de Mendoza, 12 July 2024, Scientific progress.
DOI: 10.1126/sciadv.ado6406
