Files: Biological warfare between two bacterial viruses in a genomic archipelago sheds light on the spread of CRISPR-Cas systems

CRISPR-Cas systems are acquired immunity systems of bacteria and archaea that prevent infection by viruses and other mobile genetic elements. It is currently known that this defense system has also been co-opted by the same viruses. The most studied case is a Vibrio cholerae virus that uses a CRISPR-Cas system against another satellite virus, which by contrast usually prevents its infection. We have discovered a new virus in the bacterium Acinetobacter baumannii that goes further by integrating the CRISPR-Cas system into an integration hotspot of the host genome. Once integrated, this could prevent the infection of the most frequent viruses in this bacterial species, especially one that competes with the CRISPR-Cas system itself for the same integration site. This latter virus is prevalent in strains of the species belonging to the so-called Global Clone 2, which causes the most frequent outbreaks worldwide. Knowledge of this new viral warfare involving CRISPR-Cas systems could be useful in the fight against infections caused by bacteria. But it would also shed light on the way in which these defense systems expand in bacteria.