Viruses: are they aliens that shaped our genetic destiny and could there be any fossilised on Mars?

When we think of extraterrestrial life we tend to think of Star Trek’s Klingons and Vulcans, or plants and animals or at the very least, bacteria.

But it’s possible, scientists say, that we should be paying at least as much attention to viruses.

Scientists may debate whether viruses are truly alive but, however we classify them, our own planet has an estimated 10³¹ of them (that’s a “1” followed by 31 zeros), says Penelope Boston, director of NASA’s Astrobiology Institute at NASA Ames Research Center, Moffett Field, California.

These viruses play an enormous role not just in diseases like COVID-19, but in the emerging field of astrovirology.

Viruses and similar pre-organisms act as “gene movers” which can radically affect the evolution of life by shuffling around large blocks of genes all at once, Boston reported this week at the 2022 Astrobiology Science Conference (AbSciCon22), in Atlanta, Georgia.

It has been suggested, for example, that viruses played a role in bringing photosynthesis to bacteria that did not previously have it.

Another speaker at AbSciCOn22, Rachel Whitaker, a microbiologist at the University of Illinois, Urbana, noted that a virus may have endowed early hominids with the gene for syncytin, a protein that helps a developing embryo attach to the uterus and create the placenta. Were it not for this ancient virus, you and I might not exist.

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Whitaker says that in the earliest stages of the evolution of life, before the evolution of the cell, scientists believe genes could have come and gone between our most ancient ancestors in a process known as lateral gene transfer in which anyone and everyone could easily swap genetic material with their neighbors.

Then the cell developed; and, in a step called the “Darwinian threshold” the process switched from sharing genetic material willy-nilly with your neighbors to getting your genes from your parents.

In theory, that should have substantially slowed the progress of evolution, Whitaker says. And in most cases, it did. Unless a virus was involved. Viruses, she says, had the ability to create a pandemic of change (a phrase she does not use lightly in today’s post-COVID-19 world) in which one could insert itself permanently into an organism’s genome and change its metabolism practically overnight.

Syncytin is an ancient example, but the process continues even today. Whitaker’s own research involves bacteria living in hot springs in regions as diverse as Kamchatka, Russia, and Lassen National Park, California.

“When you look at genomes,” she says, “you see signatures of lateral transfer. You see islands of genes coming and going out of nowhere.”

What this means for life on Earth is still uncertain, but one of Whitaker’s most interesting findings is that bacteria infected with a certain type of virus carry with them the ability to create toxins which kill bacteria not infected with that virus. In other words, the virus has improved its host’s ability to survive, thrive, and dominate.

“That leads to a really different type of evolution than we would have thought of,” Whitaker says. “This means that evolution is infectious.”

Other astrobiologists are impressed, but not quite sure how to incorporate this into their search for extraterrestrial life.

Boston, however, believes that this type of thinking might prove highly relevant to Mars sample returns, once they get back to Earth. “It may be possible that viruses can be fossilised,” she says.

Not that she’s predicting viruses will be found in Martian rocks once they are brought back to Earth. But given the importance they have played on Earth (and as anyone who has survived COVID-19 knows, still do), ignoring them elsewhere would be a mistake.

“In astrobiology keeping an open mind is essential,” Boston says.