Abstract
Staphylococcus aureus is a foodborne pathogen that causes food contamination and food poisoning, which poses great harm to health, agriculture and other hosts. Clustered regularly interspaced short palindromic repeats (CRISPR) are a recently discovered bacterial immune system that resists foreign genes such as phage DNA. This system inhibits the transfer of specific movable genetic elements that match the CRISPR spacer sequences, thereby preventing the spread of drug-resistant genes between pathogens. In this study, 57 CRISPR loci were screened from 38 strains of S. aureus based on the CRISPR database, and bioinformatics tools were used to investigate the structural features and potential functions of S. aureus CRISPR loci. The results showed that most strains contained only one CRISPR locus, a few strains contained multiple loci with sparsely distributed sites. These loci mainly included highly conserved direct repeat sequences and highly variable spacer sequences, as well as polymorphic cas genes. In addition, the analysis of secondary structure of direct repeat RNA showed that all sites can form stable RNA secondary structure. The results of constructing phylogenetic tree based on spacer sequence showed that some strains contained a high degree of phylogenetic relationship, while the differences among other strains in evolutionary processes were quite obvious. Of the 57 CRISPR loci identified, only the cas gene was found near the 4 CRISPR loci.
Highlights
In the past, it was known that vertebrates have the ability to resist and eliminate foreign pathogens, and could form a highly effective secondary immune mechanism to prevent the re-invasion of pathogens
The different S. aureus strain genomes were searched by the National Center for Biotechnology Information (NCBI) nucleotide database with default parameters; S. aureus Clustered regularly interspaced short palindromic repeats (CRISPR) loci were searched by the CRISPR Finder server (E-value ≤ 0.001)(Last updated on May 9, 2017)
22 strains of S. aureus contained only one CRISPR locus, 14 strains of S. aureus contained 2 CRISPR loci, and the other 2 strains contained 3 and 4 CRISPR loci. This was in comparison to other CRISPR loci on the distribution of the number of species was rare, it came down to the fact that the study of the S. aureus CRISPR system was not extensive enough, there may be some CRISPR loci hidden in the large number of suspicious CRISPR sequences
Summary
It was known that vertebrates have the ability to resist and eliminate foreign pathogens, and could form a highly effective secondary immune mechanism to prevent the re-invasion of pathogens. When the exogenous phage invaded again, this prokaryotic immune system used characteristic genes (spacers) to rapidly target and recognized foreign DNA. CRISPR Loci in 38 Staphylococcus aureus with the participation of a Cas protein complex, the invading phage DNA sequence was targeted and interfered, and the recognized foreign DNA was excised to eliminate exogenous invasion. The prokaryotic immune system, both acquired and heritable, is widespread in about 47% of bacteria and 84% of archaebacterial, which truly documents the pathways of bacterial evolution and the history of confrontations with foreign invaders (such as phages) (Lillestøl et al, 2006; Wakefield et al, 2015; Yang et al, 2015). It is tempting to speculate that CRISPR, as prokaryotic immune system, may be closely related to the high environmental adaptability of S. aureus (Schröder et al, 2013)
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