Viral viruses that have been recently discovered may offer clues about the evolution of complex life on Earth

Viral viruses that have been recently discovered may offer clues about the evolution of complex life ...

Researchers at The University of Texas at Austin have discovered "fingerprints" of mysterious viruses hidden in an ancient group of microbes that may include the origins of all complex life on Earth, from fungi to plants to humans, in a trio of studies published on June 27 in the journalNature Microbiology.

Ths discovery is significant; it explores the possibility that viruses were crucial to the evolution of humans and other complex life forms.

These microbes named Asgard archaea after the abode of the gods in Norse mythology are usually found in the frigid sediments deep in the ocean and in boiling springs, and evolved on Earth before the firsteukaryoticcells, which carry theirDNA inside a nucleus.

Some scientists have speculated that viruses may have played a role in the first stages of life following the Asgard archaea. They may have even given rise to some of the first DNA precursors, but until now, no Asgard-infecting viruses have been discovered.

"These are the first investigations investigating Asgard archaeal viruses; there was nothing known prior," Susanne Erdmann, the group leader of the Max Planck Institute for Marine Microbiology in Bremen, Germany, who was not involved in the studies, told Live Science. In the future, this line of research may reveal whether or how viruses were involved in the development of eukaryotic cells on Earth.

'An adaptive immune system'

Scientists sought for evidence of viral infection embedded in the DNA of Asgard archaea in the form of viral DNA called "CRISPR spacers."

Most people who think of CRISPR relate it to the famous gene-editing tool that allows scientists to manipulate genetic sequences easily, according to Rambo. This tool was originally developed from the natural defense mechanisms of bacteria and archaea.

CRISPR is a term for a region of DNA that is made up of short, repeated sequences with "spacers" sandwiched between each repeat. Interestingly, bacteria and archaea steal these spacers from viruses that infect them, and the cells maintain a stored archive of viral DNA that helps them recognize the viruses should they attack again.

"It's an adaptive immune system that remembers these previous infections," Rambo said. He is now a postdoctoral fellow at the USDA's Agricultural Research Service.

Rambo and his colleagues had hunted for DNA spacers in Asgard archaea specimens collected from sediments near hydrothermal vents, roughly 1.25 miles (2 kilometers) beneath the water's surface in the Guaymas Basin in the Gulf of California.

The researchers matched the spacers they found to longer sections of viral DNA collected from the deep-sea environment.

Many more Asgard-infecting viruses have yet to be discovered.

Working with viral DNA, the scientists could deduce what sorts of proteins the various genes encode for and how the viruses might function.

Erdmann noted that the functions of the majority of the viruses are still unknown. Also, many more Asgard-infecting viruses are yet to be discovered.

By growing Asgard archaea in the lab, these hidden viruses might be discovered. "However, culturing Asgard archaea has been proved to be very difficult," Erdmann said. It took 12 years for one research group to develop Asgard archaea.

CRISPR spacer matching is probably the most efficient way to find more viruses, but their role in the development of organisms, including humans, may grow more clearer, according to Krupovic.

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