Ancient microbes offer clues to the evolution of complex life

A new study published in Scientific progress A surprising discovery in the evolutionary history of complex life. Researchers at Queen Mary University of London have discovered that a single-celled organism, a close relative of animals, harbors the remains of ancient giant viruses embedded in its own genetic code. The discovery sheds light on 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. By analyzing the Amoebidium genome, researchers led by Dr. Alex de Mendoza Soler, a senior lecturer at Queen Mary’s School of Biological and Behavioural Sciences, discovered a surprising abundance of genetic material 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 hidden in the DNA of Amoebidium,” says Dr. de Mendoza Soler. “These viral insertions are potentially dangerous, but Amoebidium seems to control them by chemically silencing them.”

The researchers then investigated the extent of this phenomenon. They compared the genomes of several Amoebidium isolates and found significant variation in viral content. This suggests that the process of viral integration and silencing is continuous and dynamic.

“These results challenge our understanding of the relationship between viruses and their hosts,” says Dr. de Mendoza Soler. “Traditionally, viruses have been thought of 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 made possible by chemically taming the DNA of these intruders.”

Moreover, the discoveries made about Amoebidium offer interesting parallels with how our own genomes interact with viruses. Like Amoebidium, humans and other mammals have remnants of ancient viruses, called endogenous retroviruses, embedded in their DNA.

While these remnants were previously considered inactive junk DNA, some may now be useful. 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.