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

In the fight between bacteria and viruses, who should we bet on? The result will depend on the combat arsenal that everyone has at the moment.

And the fact is that while a person has a constant number of genes in his genome throughout his life, in bacteria it is very different. There are bacteria created using exclusive genes, some of which are real weapons of war. Sometimes one of these weapons allows them to “graft” themselves against the viruses that attack them and thus become immune to their attacks.

For their part, viruses can carry various other military devices, some of which are designed to prevent bacterial vaccines from fulfilling their mission.

What are the weapons of bacteria?

Bacteria attack specific viruses called bacteriophages (bacteria eaters). Bacteria can fight these viruses in a variety of ways. First, they can tag their own genome with a characteristic pattern, so they can tell when an unknown genome appears. These are the so-called restriction-modification systems, which are present in more than 80% of bacteria.

Another defense strategy found in bacteria is altruistic suicide or abortive infection. In this case, the bacterium kills itself, preventing further spread of the virus. These systems are present in less than 20% of bacteria, and while they won’t ultimately save humans, they will protect the population.

Finally, we have CRISPR-Cas “vaccination” systems present in 40% of bacteria, very popular in recent times due to their revolutionary use in biotechnology. In this case, when a virus enters, the system shreds its genome and stores the fragments in the bacterial genome. These fragments work like a vaccine, allowing him to more effectively recognize and attack the same virus the next time he encounters it.

What are the weapons of viruses?

Of course, viruses always fight back. There are viruses that modify their genome to cheat the restriction-modification and abortive infection systems. There are also those that have weapons such as anti-CRISPR genes that interact with the CRISPR-Cas systems to prevent them from working. So they don’t let the vaccine stop them.

In addition, another battle is taking place between the “brothers”: viruses also fight other viruses. For example, there are defective or defective viruses called satellites that lack the genes to build their genome envelope or capsid. This capsid allows them to travel in search of new bacteria to infect. The lack of an envelope in these satellite viruses is solved by using an envelope created by other viruses called assistanton which they parasitize. They throw such a face at it that a small satellite virus often modifies the shell of the virus. assistantso that only their genome gets inside and not your own assistant. Well, the virus assistant He does not always sit idle: sometimes he resorts to the CRISPR-Cas vaccination system, which recognizes the satellite virus and prevents him from using it.

How the bacterial arsenal is built

The key question is: what makes a bacterium or a virus have this weapon or not? It depends on the rest of the gene repertoire it contains. In so-called superbugs that cause nosocomial infections and are highly resistant to antibiotics, such as Acinetobacter baumannii or Pseudomonas aeruginosaWe recently discovered that those who purchase CRISPR-Cas systems often have entry gates for certain viruses on their surface.

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

Who will win then?

Once you see that neither bacteria nor viruses sit idle and are constantly evolving, attacking and defending themselves, it becomes increasingly difficult to bet on a fight between them. So I would say that the biggest beneficiary of this fight will be the spectator himself. Yes, yes, reader, me and other people.

Watching fights between bacteria and viruses, we can learn the whole arsenal of weapons of both. And this allows you to more effectively deal with superbugs.

Because bacterial viruses do not infect human cells, they have long been studied as an alternative to antibiotics. In fact, in the countries of Eastern Europe they have been used for almost a century in the so-called phage therapy. Thus, the current decline in the effectiveness of antibiotics has made this strategy a relevant alternative to consider, as described in the book. The Perfect Predatorwhich tells a real story.

In conclusion, the battles between bacteria and viruses are a spectacle that always surprises us and from which science is always ready to learn lessons in order to find solutions to humanity’s great problems.

Antonio J. Pérez Pulido, University Professor and Researcher in Bioinformatics, Pablo de Olavide University

This article was originally published on The Conversation. Read the original.