In the “War of the Worlds” by Herbert Wells Martian invaders were defeated by the common cold, which none of the sides took into account. Could something similar happen to the astronauts who will land on Mars? What if the first extraterrestrial life form humans will come into contact with will be viruses? These issues are posed in the journal Astrobiology by Dale Griffin.

What do we know about viruses?

Biologists do not consider viruses living beings. They are smaller than bacteria and cannot reproduce themselves: that is why to survive they need to invade a cell and use its genetic tools.

Nevertheless, it is viruses that rule the world: right now on earth, there are 10 million trillion viruses and one in ten lives in the oceans. Since their replication is totally dependent on cellular life, wherever there are cells, there are also viruses.

Mr. Griffin, a microbiologist at the U.S. Geological Survey, thinks that it is probable to face a similar situation on other inhabited planets:

I think the evolution of cellular life on other planets takes place as well as on Earth. And next to the cells there will be also a mind-blowing amount of viruses.”

He notes that astrobiologists are not very friendly with this idea. This is partly due to the fact that the studies of recent years concern only the viruses which cause diseases in humans and animals. It is understandable because studying viruses is no easy matter.

Only recently, there appeared the molecular tools that made it possible to determine the number and degree of diversity of the viruses in the world“, says Mr. Griffin.

Another problem is that the earthly viruses in most cases have become symbionts of their hosts, that is why, for example, a person cannot catch a cold from a dog and vice versa. Therefore, for a detailed study of viruses, it is necessary to grow a host cell in the laboratory (usually bacteria are used for this purpose), but the hosts of many viruses are still unknown. As a result, the study of viruses goes slowly.

What about extraterrestrial viruses?

But times change, and Mr. Griffin believes that it is time to think about extraterrestrial viruses. Biologist Kenneth Stedman of Portland State University (USA) is ready to support his colleague.

Viruses obviously have a strong influence on life on earth,” he said. “The question is how important viruses are for life, but definitely without them, it would be different.”

It is unknown when viruses appeared on Earth, but they certainly originated in ancient times. Perhaps they were the factor that pushed evolution to create cells.

Intruding into the cell, the virus unpacks its own genetic material and tries to attach it to the cell genome. If replication is successful, the virus captures a bit of genetic information and transfers it from cell to cell, from body to body.

Of course, viruses are harmful, but not always. For example, if a cell is damaged by ultraviolet radiation, a virus that has genes resistant to UV light can pass them to the cell, and it will try to heal the wounds. Conversely, damaged viruses can restore the ability to replicate, if the cell is flooded with numerous viruses that got the opportunity to exchange genetic information and thereby produce a complete viral genome.

As a result, viruses are extremely hardy. They are persistent, well-adapted to the new conditions, and are able to stay long in hibernation until better times. While outside a host cell viruses are inert, they can survive in extreme conditions.

For instance, viruses have been found in the water of hot springs of Yellowstone National Park in the United States at a temperature of 93° C. At the same time they survive in very salty water at a temperature of -12° C, while the influenza virus is stored in labs at -70° C. In the absence of cell, water is not necessary, and viruses simply remain inactive, quietly waiting for entering the cell.

What does all this mean?

Imagine a planet where life has long disappeared, for example, Mars. Although it is not yet proven that there existed life in the hypothetical period when our neighbor planet was warm and humid, we will assume that the primitive organisms were born and were accompanied by viruses.

Since most viruses on Earth are specific to the host, Mr. Griffin argues that on other planets the situation will be the same. But then Martian life extinct (or nearly extinct), the viruses got a serious problem. If they continue to be specific, they will disappear along with their hosts. If they acquire the ability to penetrate into any cell and exchange genetic information with it, they will survive.

Therefore, it is possible that on Mars (if there is anything left), there are organisms that are waiting for any form of life to get there. Perhaps the equipment sent to Mars to search for life should also be ‘taught’ to detect such organisms.

Mr. Griffin has a few ideas about how to do it. There are concentrators based on microelectromechanical systems used in chromatography and spectroscopy. They are used in microscopic separators, nucleic sequencers, and microscopes.

So it is possible to take a soil sample and look for organisms similar to viruses. At the same time, we would find cells, decipher samples of DNA and RNA (or whatever they have), and understand how much they are similar to terrestrial counterparts.

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