Bacteriophages or phages are viruses that infect bacteria. Remarkably, they are the most abundant biological entities on the biosphere. There is a debate about if phages (or viruses) are organisms or not. Some people do not consider phages as organisms because phages can not reproduce autonomously. Other people do consider viruses as organisms with a two-stage life cycle: intracellular and extracellular. Phages are composed by a nucleic acid molecule (DNA or RNA) surrounded by a coat of proteins. To reproduce their genetic material as well as to make more proteins, they need to infect a bacterial cell and as a consequence of the phage’s cycle the bacterial cell dies. In order to escape from the phage, bacterial cells evolve and in order to infect bacteria, phages evolve too. This process is known as evolutionary arms race. Therefore, we find in nature some bacteria that are resistant to some phages. Sometimes the phage-bacteria relationship becomes symbiotic in the sense that the phage genome integrates into the bacterial genome, so they benefit from each other.
The AMR (antimicrobial resistance) crisis that we are facing is urging us to develop alternative treatments against bacterial infections. Phage therapy is now of great interest. We are interested in understanding the complex relationship that phages and bacteria might establish as well as in designing phages as biotechnological and therapeutic tools.