Characterization of CRISPR Spacer and Protospacer Sequences in and Its Bacteriophages.

The bacterium is the causative agent of American foulbrood, the most devastating bacterial disease of honeybees. Because is antibiotic resistant, phages that infect it are currently used as alternative treatments. However, the acquisition by of CRISPR spacer sequences from the phages could be an obstacle to treatment efforts. We searched nine complete genomes of strains and identified 714 CRISPR spacer sequences, of which 384 are unique. Of the four epidemiologically important strains, three of these have fewer than 20 spacers, while one strain has over 150 spacers. Of the 384 unique spacers, 18 are found as protospacers in the genomes of 49 currently sequenced phages. One strain does not have any protospacers found in phages, while another has eight. Protospacer distribution in the phages is uneven, with two phages having up to four protospacers, while a third of phages have none. Some phages lack protospacers found in closely related phages due to point mutations, indicating a possible escape mechanism. This study serve a point of reference for future studies on the CRISPR-Cas system in as well as for comparative studies of other phage-host systems.