“Backup Weapon Released When CRISPR Is Disabled”: Two-Tiered Defense System Discovered in Bacteria

The CRISPR system, of which two classes and 46 subtypes have been identified to date, has been found to act as a “commander in chief” that regulates other immune genes in Neisseria bacteria. Under normal conditions, the CRISPR-Cas complex suppresses the expression of other defense genes, but when CRISPR is disabled by infection with a virus (phage), the suppression is lifted and a backup defense system is activated. The discovery is expected to contribute to the development of phage therapies that kill antibiotic-resistant bacteria and to the enhancement of industrial bacterial strains.