Science | August 22, 2017 12:04 pm

Mystery Microbe Could Tell Us More About the Origins of Viruses

The Antarctic microorganism is 'host to a fragment of DNA that can build a capsule around itself.'

A strange Antarctic microbe could just offer a huge clue to one of evolution’s biggest mysteries: the origin of viruses. According to New Scientistthe microorganism is “host to a fragment of DNA that can build a capsule around itself.”

Viruses themselves are not alive because they are not made from cells. Instead, a typical virus is a “small piece of genetic material encased in a shell called a capsid.” However, if the virus enters a living cell, it starts copying itself. For decades, biologists have been unsure where viruses come from.

But now, Richard Cavicchioli of the University of New South Wales in Australia and his colleagues have found this new microorganism in the lakes of the Rauer Islands off the coast of Antarctica. It is an “archaean: a kind of single-celled organism that looks like a bacterium, but actually belongs to a separate domain of life.” They have named it Halorubrum lacusprofundi R1S1.

Team member Susanne Erdmann searched for viruses within the organism’s cells. She found a plasmid, which are small fragments of DNA. They often carry a gene that is somehow useful to the cell. The plasmid Erdmann found is unusual, because they allow pR1SE to leave its host cell and seek out new hosts. This means that it looks and acts like a virus but it has no telltale virus genes.

Cavicchioli now suggests that viruses could have evolved from plasmids just like this one. This suggestion lines up with other evidence on the origin of viruses. There are three leading ideas: viruses originated before cells, some cells evolved simpler forms and became viruses or, genes “escaped” from cells and became viruses. The third hypothesis has gained more support throughout the years.

Patrick Forterre of the Pasteur Institute in Paris says that the evidence implies these escapes began early in life’s history.

“Traditionally the escape hypothesis has been associated with the idea that viruses are recent,” he said to New Scientist. “Now the escape hypothesis should be viewed in a broader context.” The first viruses may have escaped from some of the first cells on Earth.