Biologists have found evidence that viruses have some form of collective intelligence and are able to recognize the "marks" that their competitors and relatives leave in cells, and to guide them when making decisions, according to an article published in the journal Nature.
“These bacteriophages (viruses that infect bacteria) contain two programs of behavior. One makes the cell produce a huge number of copies of itself and launches a self-destruction program in it, and when the second is turned on, it integrates into its DNA and goes into a “deep underground” with the possibility of revival in the future,”explains Nonia Pariente, molecular biologist and editor of the journal Nature Microbiology.
Soldiers of eternal war
Diseases and infections are not something that only humans and other multicellular creatures suffer - there has been a continuous war for survival between bacteria and viruses for several hundred million years. Traces of this war can be found everywhere - each milliliter of sea water contains up to a billion "fighting viruses" - bacteria, and about 70% of marine microorganisms are infected with them.
Over billions of years of evolution, viruses have learned to bypass the attention of microbial defense systems, and the latter have developed a kind of genetic "antivirus", the CRISPR-Cas9 system, which finds traces of viral DNA in the genome of a microbe and forces it to commit suicide to protect neighboring bacteria. Viruses responded to these "evolutionary defenses" by creating an anti-antivirus that suppresses CRISPR-Cas9, and the biological arms race continued.
Rotem Sorek of the Weizmann Institute of Science in Rehovot, Israel and his colleagues found another very interesting example of a "weapon" invented by viruses by studying how the phi3T bacteriophage, infecting common bacilli (Bacillus subtilis), works.
Initially, scientists tried to understand a completely different thing - how microbes notify each other about the presence of a virus and prepare to repel its attack. Scientists believed that infected bacteria release special signaling molecules into the environment that signal to other microbes in their colony about danger.
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To test this, Sorek and his colleagues raised a colony of bacilli, infected them with phi3T, and then filtered the liquid that the microbes released during the infection of the colony. The biologists added part of this solution to the new colony of bacteria, suggesting that the signaling molecules that their dead friends released into the nutrient medium would prepare them for a new attack of viruses and protect them from infection. The reality turned out to be completely different.
Secret signals
It turned out that the short protein molecules arbitrium that biologists isolated from this solution were in fact intended for viruses to communicate with each other, not bacteria, and their "authors" were not microbes, but their uninvited guests.
These molecules, as shown by the experiments of Israeli geneticists, make the virus "switch" from one reproduction program to another. In the presence of arbitrium, viruses “go underground”, inserting themselves into the DNA of bacteria instead of proliferating in them and destroying cells.
The program switch occurs because arbitrium blocks the work of the viral protein AimR, which is responsible for starting the procedure for multiplying viral DNA and dissolving the walls of the bacteria.
Why do viruses need it? This signaling system, scientists explain, works as a kind of collective intelligence of viruses, which allows them to flexibly coordinate their behavior. When there are few viruses, it is more beneficial for them to actively multiply, infecting new bacteria and killing them, but over time there are too many of them and the bacteria begin to collectively respond to infection, or the number of bacilli drops to extremely low values.
At this point, the viruses switch to an alternative infection program, using signals like arbitrium, and "hide in the crowd", waiting for a new opportunity for infection. Sorek says his team has found more than a hundred other molecules similar to arbitrium and AimR in other bacteriophage viruses, suggesting that many, or even all, viruses are able to "communicate" with their own kind.
It is possible that similar systems exist in viruses infecting humans, and their presence could explain how HIV and a number of other retroviruses hide in cells while trying to expel them from the body. If scientists manage to find a molecule that will make HIV “dig in” in the cell forever and not leave there, then the problem of fighting it will be solved.
