ABSTRACT

Bacteriophages are viruses that infect bacteria by injecting their viral DNA/ RNA into the host cell, which often results in bacterial death. But in some instances, the phages will insert their genome into the bacterial chromosomes that benefits the cells by providing new traits. Clustered regularly interspaced short palindromic repeats (CRISPR) systems, are a self-defensive mechanism bacteria have evolved to protect themselves from viral DNA. CRISPR systems contains three distinct parts; Cas genes, a leader sequence and repeat sequences regularly interspersed with spacer sequences, which can number in the 100s. The system functions by recognizing new viral DNA stored in spacer sequences (memory of prior viral infections) and targeting the new viral DNA for degradation. To understand how this system has evolved in bacteria we analyzed members of the genus Yersinia that contains many human pathogens that cause food poisoning and bubonic plague. Our bioinformatics analysis identified CRISPR systems in 10 Yersinia species. By utilizing the NCBI genomic data base and the program CRISPRDetect, we examined four species in detail; Yersinia pestis, Y. pseudotuberculosis, Y. intermedia, and Y. enterocolitica. We found depending on the species a very different complement of CRISPR system was present. Among Y. pestis and Y. pseudotuberculosis strains, Type I-F CRISPR systems were prevalent whereas among the other two species only a limited number of strains contained a system. The majority of systems had multiple spacer sequences indicating that they are active systems.