Human defenses against viruses first evolved billions of years ago, a study suggests: ScienceAlert

Microbes that emerged billions of years ago may have made our immune system what it is today.

New research from the University of Texas (UT) suggests that complex organisms like us may not have been as well equipped to fight viruses if they had not had the ability to given to us by our single-celled ancestors.

Long before multicellular life evolved, our planet was home to a widespread group of primordial microbes.

The descendants of these ancient microbes still alive today were only discovered in 2015 through traces of her DNA, deep in the ocean between Greenland and Norway. Five years later, the lurking life form – a superphylum of archaea called Asgard – was successfully grown for the first time in the laboratory.

AAt first glance, they looked very similar to bacteria under the microscope. But archaea cells are evolutionarily closer to eukaryotic life forms such as plants and animals than to their simpler microbial relatives.

Based on their genomes, some scientists believe that the Asgard archaea and our eukaryotic ancestors diverged about 2 billion years ago, paving the way for all complex life on Earth.including animals, plants, fungi, protists and most algae.

Whatever this common ancestor looked like, at some point it had to incorporate a nucleus into its basic structure. Some scientists suspect that the Asgardian ancestors evolved a nucleus from a virus that created a protective compartment called a virus factory.Mitochondria, on the other hand, could have arisen through the destruction of a bacterial ancestor.

Since very little is known today about how living archaea protect themselves from threats such as bacteria or viruses, it is difficult to investigate such hypotheses in detail.

Researchers at UT have now used an artificial intelligence program to sift through a newly expanded set of Asgard genomes to identify ancient immune defense mechanisms.

The team found that cCompared to bacteria, Asgard archaea have evolved a wide range of defense systems, some of which are also innate to eukaryotes.

Of all the defense systems in the genomes of the Asgard archaea studied, about 2 percent were linked to an immune protein, the vipersthat fights a broad spectrum of viral infections by seemingly “silencing” viral reproduction.

Today, viperin plays a role in the immune system of all complex life on Earth, suggesting that it was present in the last common ancestor of archaea and eukaryotes.

According to the new findings, eukaryotic viperins and Asgard viperins are “sister proteins and share a common ancestor.”

“Not only does it say that eukaryotes got all these rich structural proteins that we saw before in Asgards,” explains UT integrative biologist Brett Baker, “but now it also says that even some of the defense systems of eukaryotes came from Asgards.”

In addition to viperin, almost 8 percent of the Asgard archaea's defense genes analyzed were associated with argonautes. These are immune proteins that chop up DNA to stop the spread of a virus.

In all areas of life on our planetFrom archaea and bacteria to eukaryotes, argonauts act as “programmable immune systems.”

To test how these proteins work in living cells, the researchers used the genetic instructions for viperine from the Asgard archaea genomes and cloned them into Escherichia coli Bacteria. When a virus was introduced, the bacterial cells showed some signs of protection.

“Viral infections are one of the evolutionary constraints we have faced since the beginning of life, and it is crucial to always have some kind of defense,” explained Pedro Leão, who conducted the research while in Baker's lab at UT.

“When bacteria and archaea discovered tools that worked, they were passed on and are still part of our first line of defense.”

Thanks to the microbes.

The study was published in Nature communication.