Analysis of the features of 105 confirmed CRISPR loci in 487 Klebsiella variicola.

Klebsiella variicola (K. variicola), an emerging human pathogen, poses a threat to public health. The horizontal gene transfer (HGT) of plasmids is an important driver of the emergence of multiple antibiotic-resistant K. variicola. Clustered regularly interspersed short palindromic repeats (CRISPR) coupled with CRISPR-associated genes (CRISPR/Cas) constitute an adaptive immune system in bacteria, and can provide acquired immunity against HGT. However, the information about the CRISPR/Cas system in K. variicola is still limited. In this study, 487 genomes of K. variicola obtained from the National Center for Biotechnology Information database were used to analyze the characteristics of CRISPR/Cas systems. Approximately 21.56% of genomes (105/487) harbor at least one confirmed CRISPR array. Three types of CRISPR/Cas systems, namely, the types I-E, I-E*, and IV-A systems, were identified among 105 strains. Spacer origin analysis further revealed that approximately one-third of spacers significantly match plasmids or phages, which demonstrates the implication of CRISPR/Cas systems in controlling HGT. Moreover, spacers in K. variicola tend to target mobile genetic elements from K. pneumoniae. This finding provides new evidence of the interaction of K. variicola and K. pneumoniae during their evolution. Collectively, our results provide valuable insights into the role of CRISPR/Cas systems in K. variicola.