Incredible viral discovery offers clues to the origins of complex life

Origin of the artist-in-living concept

Artistic concept “Origin of Life”.

The first discovery of viruses infecting a group of microbes that may include the ancestors of all complex life has been found, scientists at the University of Texas at Austin (UT Austin) report. natural microbiology. The incredible discovery offers tantalizing clues to the origins of complex life and suggests new directions for examining 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 have cells with a nucleus called eukaryotes — arose when archaea and bacteria merged into a hybrid organism. Recent research suggests that the first eukaryotes are direct descendants of the so-called Asgard archaea. Recent research by Ian Rambo (a former graduate student at UT Austin) and other members of Brett Baker’s lab sheds light on how viruses may also have played a role in this billion-year-old story.

Viruses infecting ASGARD archaea

Comparison of all known virus genomes. Those viruses with similar genomes are grouped together, including those that infect bacteria (left) and eukaryotes (right and bottom center). The viruses infecting Asgard archaea are unique to those previously described. Photo credit: University of Texas at Austin

“This study opens a door to better elucidate the origin of eukaryotes and to understand the role of viruses in the ecology and evolution of Asgard archaea,” Rambo said. “There is a hypothesis that viruses may have contributed to the emergence of complex cell life.”

Alvin Submersible

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

Rambo refers to a hotly debated hypothesis called viral eukaryogenesis. It suggests that in addition to bacteria and archaea, viruses may also have contributed a genetic component to the evolution of eukaryotes. While this latest discovery doesn’t end this debate, it does offer some interesting clues.

The newly discovered viruses that currently infect living Asgard archaea share some similar characteristics to viruses that infect eukaryotes, including the ability to copy their own[{” 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.

Alvin Submersible in Gulf of California

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.