Incredible discovery of viruses provides clues about the complex origins of life

The first discovery of viruses that infect a group of microbes that may include Complex life ancestors Scientists at the University of Texas at Austin (UT Austin) have been found Report in Nature Microbiology. The startling discovery provides tantalizing clues about the origins of complex life and suggests new directions for investigating the hypothesis that viruses were essential to the evolution of humans and other complex life forms.

There is a well-supported hypothesis that all complex life forms such as humans, starfish and trees – which are characterized by cells with a nucleus and are called eukaryotes – arose when Archaea and bacteria fuse to form a hybrid organism. Recent Research It is suggested that the first eukaryotes are direct descendants of the so-called Asgard archaea. The latest research, conducted by Ian Rambo (a former doctoral student at the University of Austin) and other members of the Brett Baker Laboratory, also highlights the role of viruses in this billion-year history.

Comparison of all known virus genomes. These viruses with similar genomes are grouped together including those that infect bacteria (left) and eukaryotes (centre right and bottom). Viruses infecting Asgard archaea are unique from those previously described. Credit: The University of Texas at Austin

“This study opens the door to a better solution to the origin of eukaryotes and to an understanding of the role of viruses in the environment and the evolution of Asgard archaea,” Rambo said. “There is a hypothesis that viruses may have contributed to the emergence of complex cellular life.”

Researchers from UT Austin used the Alvin submersible to collect sediment and microbial samples from 2,000 meters (6,600 feet) depth in the Gulf of California. Credit: Brett Baker

Rambo points to a controversial hypothesis called the formation of viral eukaryotes. She suggests that in addition to bacteria and archaea, viruses may have contributed some genetic components to the development of eukaryotes. While this latest discovery does not settle this controversy, it does provide some interesting evidence.

Recently discovered viruses that infect live Asgard archaea have some features similar to viruses that infect eukaryotes, including the ability to transcribe them.[{” attribute=””>DNA and hijack protein modification systems of their hosts. The fact that these recovered Asgard viruses display characteristics of both viruses that infect eukaryotes and prokaryotes, which have cells without a nucleus, makes them unique since they are not exactly like those that infect other archaea or complex life forms.

“The most exciting thing is they are completely new types of viruses that are different from those that we’ve seen before in archaea and eukaryotes, infecting our microbial relatives,” said Baker, associate professor of marine science and integrative biology and corresponding author of the study.

The Asgard archaea, which probably evolved more than 2 billion years ago and whose descendants are still living, have been discovered in deep-sea sediments and hot springs around the world, but so far only one strain has been successfully grown in the lab. To identify them, scientists collect their genetic material from the environment and then piece together their genomes. In this latest study, the researchers scanned the Asgard genomes for repeating DNA regions known as CRISPR arrays, which contain small pieces of viral DNA that can be precisely matched to viruses that previously infected these microbes. These genetic “fingerprints” allowed them to identify these stealthy viral invaders that infect organisms with key roles in the complex origin story of eukaryotes.

Researchers from UT Austin used the Alvin submersible to collect sediment samples and microbes from 2000m (6600 feet) deep in the Gulf of California. Credit: Brett Baker

“We are now starting to understand the implication and role that viruses could have had in the eukaryogenesis puzzle,” said Valerie De Anda, a research associate at UT Austin and co-author of the study.

Reference: “Genomes of six viruses that infect Asgard archaea from deep-sea sediments” 27 June 2022, Nature Microbiology.
DOI: 10.1038/s41564-022-01150-8

The other co-authors of the study are Pedro Leão, a postdoctoral research fellow at UT Austin, and Marguerite Langwig, formerly a master’s student at UT Austin and currently a doctoral candidate at the University of Wisconsin-Madison. This work was supported by the Moore and Simons Foundations.