Characterization of CRISPR-Cas systems in the Haemophilus genus CRISPR-Cas in Haemophilus spp

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated (Cas) system constitutes a crucial adaptive defense mechanism in prokaryotes against foreign genetic elements. Although CRISPR-Cas systems have been characterized in numerous bacteria, the architecture and function of these systems in the Haemophilus genus remain poorly understood. This study aims to analyze CRISPR-Cas systems in 138Haemophilusstrains and investigate their function, particularly in relation to virulence factors. Results revealed that CRISPR-Cas systems were identified in 31.88% of the Haemophilusstrains. Subtype I-C was the most prevalent, followed by subtypes II-C and III-A. Repeat sequences and thecas1gene were highly conserved within the same subtype. 29.62% of spacer sequences exhibited homology to plasmids or bacteriophages. phiMHaA1 was an important target of the CRISPR-Cas system in Haemophilusgenus. The protospacer adjacent motif sequences (PAM) were determined to be 5'-TTC-3' for subtype I-C and 5'-TTT-3' for subtype II-C. Comparative analysis of virulence genes showed that CRISPR-positive strains carried more ompP2 than CRISPR-negative strains, while the distribution of hmw2C and hmw1C exhibited an opposite trend. These findings provide novel insights into the diversity and function of CRISPR-Cas systems inHaemophilusgenus and propose potential strategies for attenuating the impact ofHaemophilusvirulence factors.