The CRISPR-Cas app goes viral

[Display omitted] •CRISPR spacer content is a gold mine of information to learn about the past genetic environments of microbial populations.•Bacteria of industrial interest can be protected against phages by means of natural or engineered CRISPR immunization.•Natural and engineered CRISPR-Cas systems can be found on the genome of phages.•A century of phage research and a decade of CRISPR-Cas research provide novel opportunities to fight multi-drug resistant bacteria. If biology laboratories were smartphones, CRISPR-Cas would be the leading app. Nowadays, technology users rely on apps to communicate, get directions, entertain, and more. Likewise, many life scientists now rely on CRISPR-Cas systems to study the interactions between microbes and their viruses, to track strains as well as to modify and modulate genomes. Considering their high level of polymorphism, CRISPR arrays can increase the resolution of a microbial typing scheme. As dynamic systems, they allow the identification and the tracking of specific sequences, which is highly valuable for epidemiological studies. As a defense mechanism, they offer an opportunity to generate virus-resistant strains or even to construct strains refractory to the acquisition of specific genes. And last but not least, as customizable and transferable tools, CRISPR-Cas systems are particularly promising to fight multi-drug resistant bacteria through the engineering of phages.