In HG Wells' War of the Worlds, the Martian invaders were defeated by a fighter whom neither side took into account - the common cold.
Could something similar happen to astronauts who land on Mars? What if the first form of alien life that humans encounter were viruses? These are the questions asked by Dale Griffin in Astrobiology.
Biologists don't think of viruses as living things. They are smaller than bacteria (compare: 20-300 nm and 500-1,500 nm) and cannot reproduce themselves: for this they need to invade the cell and use its genetic tools. Nevertheless, it is viruses that rule the world. Hypochondriacs will probably shudder from the fact that there are 10 million trillion trillion viruses on Earth right now, and every tenth lives in the oceans. Since their replication is completely dependent on cellular life, it is not surprising that wherever there are cells, you will find viruses.
Mr. Griffin, a microbiologist with the US Geological Survey, believes that a similar situation will meet us on other inhabited planets: “I think the evolution of cellular life on another planet will proceed the same as on Earth. And there will be viruses next to the cells - in a mind-boggling amount."
He notes that astrobiologists are not yet very friendly with this idea. This is partly due to the fact that lately specialists have been dealing only with those viruses that cause diseases in humans and animals. This is understandable, because studying viruses is not easy.
“It’s only very recently that microbiologists have the molecular tools to measure the abundance and diversity of viruses on Earth,” says Mr Griffin. The problem is also that terrestrial viruses, in most cases, have turned into symbionts of their hosts - which 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 a bacterium plays this role), but the host (s) of many viruses is still unknown (unknown). As a result, the study of viruses on Earth is slow. This is also recognized by Chris Impey of the University of Arizona (USA), who has written several books on astrobiology: “Since most types of bacteria are difficult to grow,we still have no idea about the whole complex of symbiotic relationships between bacteria and viruses."
But times are changing, and Mr. Griffin believes it is time to think about extraterrestrial viruses. Biologist Kenneth Stedman from Portland University (USA) is ready to support his colleague. "Viruses, and this is obviously, greatly affect life on earth," he emphasizes. - The question remains about how important viruses are for life, but, definitely, life on Earth would be completely different without them. I would be surprised if they find a life without viruses, it will be a very interesting turn."
According to Mr. Griffin, the question is not whether viruses will exist where life exists (of course, we will discover life long before its accompanying viruses). We can find viruses at the initial and final stages of the evolution of life on the planet.
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It is not known when viruses appeared on Earth, but it is safe to bet that they originated in ancient times. Perhaps it was they who pushed evolution to create cells. By invading a cell, the virus unpacks its own genetic material, which it tries to attach to the cellular genome. If replication is successful, the grateful virus, lighting up, captures some genetic information and transfers it from cell to cell, from organism to organism. Gene exchange drives evolution.
Of course, viruses are harmful, but not only. For example, if a cell is damaged by ultraviolet radiation, a virus that has genes for UV resistance can pass them on to the cell and it will try to heal the wounds. Conversely, damaged viruses can restore the ability to replicate if the cell is infested with numerous viruses, which are thus able to exchange genetic information and thereby produce a complete viral genome.
As a result, viruses are extremely hardy. “They are persistent, adapt well to new conditions and are able to stay in hibernation for a long time until better times,” explains Mr. Impi. Although viruses are inert outside the host cell, they can survive in extreme conditions, and there are many examples. Let's say viruses were found in hot springs in Yellowstone National Park in the United States at 93 ° C. At the same time, they survive in very salty sea water at -12 ° C, and the flu virus is stored in laboratories at -70 ° C, and he does not complain. In the absence of a cell, water is not necessary: viruses simply remain inactive, and if they are not destroyed, for example, by radiation, they will calmly wait until they enter the cell.
Let's imagine a planet on which life has long disappeared. Let's not go far, let's take Mars. Although it has not yet been proven that life existed there in that hypothetical period when our neighbor was warm and humid, we will proceed from the assumption that primitive microorganisms had time to appear and that they were accompanied by viruses. On Earth, most viruses are host-specific, and Mr. Griffin claims that will be the same on other planets. But then Martian life became extinct (or almost extinct), and the viruses faced a serious problem. If they remain as specific, they will disappear along with their masters. If they can acquire the ability to penetrate the first cell they come across and exchange genetic information with it, they will survive.
Therefore, it is quite possible that on Mars (if there is anything else left at all), such universal soldiers are waiting for us, which represent a serious biological hazard. Probably, by sending equipment there to search for life, you need to teach it to detect viruses as well.
Mr. Griffin has a couple of ideas on how to do this. There are concentrators based on microelectromechanical systems that are used in chromatography and spectroscopy. They will be helped by microscopic separators, nucleic acid sequencers and microscopes. Take a soil sample and look for formations that look like viruses. At the same time, we will find cells, decipher sections of DNA and RNA (or whatever they have) and understand how similar they are to Earth's counterparts.
There is at least one other place in the solar system where viruses will become the same; you just have to wait. In about a couple of billion years, the brightness of the Sun will increase, the Earth will heat up, plants will dry up and die, the oceans will boil away, life will disappear. Viruses alone are not going anywhere. In conditions of a shortage of cellular material, they will learn to love their neighbor and will exchange genes with just anyone. Altruism - this is the note on which the song of life will end when the Sun becomes so hot that even viruses cannot stand it. The unison of viruses and cells - this is where evolution begins and ends, although billions of years of terrible competition pass between these stages.
"The study of viruses has the potential to revolutionize astrobiology," says colleague Impi. "Griffin's work could be a good starting point."