Ancient microbes offer clues to how complex life evolved

By Dr. Tim Sandle
July 27, 2024
DIGITAL JOURNAL

Microbiologist Yuen Kwok-yung, who helped Hong Kong battle SARS and Covid-19, fears a future pandemic could be far worse - Copyright AFP ISAAC LAWRENCE

The study of ‘ancient’ microbial life provides clues as to how humanity’s single-celled ancestors mixed viral DNA into their own genetic code. This adds to our understanding of the evolutionary process.

Researchers from Queen Mary University of London have discovered that a single-celled organism, a close relative of animals, harbours the remnants of ancient giant viruses woven into its own genetic code.

This finding increases our understanding of how complex organisms may have acquired some of their genes and highlights the dynamic interplay between viruses and their hosts.

The study focused on a microbe called Amoebidium, which is a unicellular parasite found in freshwater environments. Amoebidium species attach to the exoskeleton of freshwater aquatic arthropods such as midge larvae and water fleas.

By analysing Amoebidium‘s genome, the researchers led by Dr Alex de Mendoza Soler, found an abundance of genetic material originating from giant viruses – these are 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,” de Mendoza Soler explains.

He adds: “These viral insertions are potentially harmful, but Amoebidium seems to be keeping them in check by chemically silencing them.”

The scientists investigated how widespread this phenomenon might be. They compared the genomes of several Amoebidium isolates and found significant variation in the viral content. This outcome suggests that the process of viral integration and silencing is ongoing and dynamic.

According to 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.”

The researcher explains further how 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 our DNA. While these remnants were previously thought to be inactive “junk DNA,” some might now be considered to be beneficial.

Unlike the giant viruses found in Endogenous Retroviruses are much smaller, and the human genome is significantly larger. It is hoped that future research will be able to explore these similarities and differences to understand the complex interplay between viruses and complex life forms.

The research appears in the journal Science Advances, titled “DNA methylation enables recurrent endogenization of giant viruses in an animal relative.”