Discovery of Ancient Giant Virus Remnants Offers New Clues to the Origins of Complex Life

A new study 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 discovery reveals that these viral genes, though potentially harmful, are kept inactive by chemical processes within Amoebidium’s DNA, suggesting a more intricate relationship between viruses and their hosts, which could impact our understanding of genetic evolution in other organisms, including humans.

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
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.”

Amoebidium appalachense cells stained for DNA (in blue, showing the nucleus) and actin (in green), highlighting the cell membranes in the cellularization step of the colony. Credit: Alex de Mendoza

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