Bacteria are vaccinated against viruses and viruses are vaccinated against other viruses.

In a fight between bacteria and viruses, who should we bet on? The result will depend on the war arsenal that each one possesses at each moment.

And it is that, while the human being presents a constant number of genes in his genome throughout his life, in bacteria it is very different. There are bacteria that are made with exclusive genes, some of which are real weapons of war. Sometimes, one of these weapons allows them to be “vaccinated” against the viruses that attack them and thus become immune to their attacks.

For their part, viruses can carry other different war devices, some designed to prevent bacterial vaccines from fulfilling their mission.

What are the weapons of bacteria?

Bacteria are attacked by specific viruses called bacteriophages (bacteria eaters). Bacteria can fight against these viruses various forms. For one thing, they can mark their own genome with a characteristic pattern, so they can tell when an unknown genome comes in. It is what are called restriction-modification systems, present in more than 80% of bacteria.

Another defense strategy found in bacteria is altruistic suicide, or abortive infection. In this case, the bacteria kills itself, preventing the virus from progressing further. These systems appear in less than 20% of bacteria, and although they would not ultimately save the individual, they would protect the population.

Finally, we have the CRISPR-Cas “vaccination” systems, present in 40% of bacteria, very popular lately due to their revolutionary use in biotechnology. In this case, when a virus enters, the system chops up its genome and saves fragments in the bacterium’s genome. These fragments work like a vaccine, allowing him to more efficiently recognize and attack the same virus the next time he encounters it.

And what are the weapons of viruses?

Of course, viruses always fight back. There are viruses that modify their genome to deceive restriction-modification systems and abortive infection systems. There are also those who have weapons like genes anti-CRISPR, which interact with CRISPR-Cas systems to prevent their operation. In this way, they prevent the vaccine from stopping them.

Additionally, there is another battle between “brothers”: viruses also fight against other viruses. For example, there are defective or defective viruses called satellite, which lack genes to make the envelope for their genome or capsid. This capsid allows them to travel to find new bacteria to infect. The lack of envelope of these satellite viruses is solved by taking advantage of the envelope produced by other viruses called helper, to which they parasitize. They throw such a face at it that the small satellite virus often modifies the envelope of the helperso that only their genome fits inside and not their own helper. Well, the virus helper It doesn’t always sit idle: sometimes it resorts to a CRISPR-Cas vaccine system, which recognizes the satellite virus and prevents it from taking advantage of it.

How the bacterial arsenal is built

The key question is: what makes a bacterium or a virus have these weapons or not? It depends on the rest of the repertoire of genes that it contains. In the so-called superbugs, which cause hospital-acquired infections and are super-resistant to antibiotics, such as Acinetobacter baumannii o Pseudomonas aeruginosa, we have recently found that those that acquire CRISPR-Cas systems usually have entry gates on their surface for certain viruses.

If the bacterium has a unique protein on its surface that allows it, for example, to expel a certain antibiotic more efficiently, this will be an advantage for it. But if this protein is in turn a gateway for a specific virus, the bacterium will need to be protected with a vaccination system.

Who wins then?

Once seen that neither the bacteria nor the virus sit idle, and constantly evolve to attack and defend themselves, it becomes more difficult to bet on a fight between the two. So I would say that the biggest beneficiary in this fight would be the spectator himself. Yes, yes, the reader, myself and the rest of human beings.

Observing the fights between bacteria and viruses, we can know the entire weapons arsenal of both. And this allows us to fight more efficiently against superbugs.

Because bacterial viruses do not infect human cells, they have long been studied as an alternative to antibiotics. In fact, in Eastern European countries they have been used for almost a century in what is known as phage therapy. Thus, the current decline in the effectiveness of antibiotics has made this strategy a present alternative to take into account, as described in the book The Perfect Predatorin which a real case is told.

In conclusion, the battles between bacteria and viruses are a spectacle that always surprises us and from which science is always willing to learn to provide solutions to the great problems of the human being.