Analysis of the type II-A CRISPR-Cas system of Streptococcus agalactiae reveals distinctive features according to genetic lineages

Abstract

CRISPR-Cas systems (clustered regularly interspaced short palindromic repeats/CRISPR-associated proteins) are found in 90% of archaea and about 40% of bacteria. In this original system, CRISPR arrays comprise short, almost unique sequences called spacers that are interspersed with conserved palindromic repeats. These systems play a role in adaptive immunity and participate to fight non-self DNA such as integrative and conjugative elements, plasmids, and phages. In Streptococcus agalactiae, a bacterium implicated in colonization and infections in humans since the 1960s, two CRISPR-Cas systems have been described. A type II-A system, characterized by proteins Cas9, Cas1, Cas2, and Csn2, is ubiquitous, and a type I–C system, with the Cas8c signature protein, is present in about 20% of the isolates. Unlike type I–C, which appears to be non-functional, type II-A appears fully functional. Here we studied type II-A CRISPR-cas loci from 126 human isolates of S. agalactiae belonging to different clonal complexes that represent the diversity of the species and that have been implicated in colonization or infection. The CRISPR-cas locus was analyzed both at spacer and repeat levels. Major distinctive features were identified according to the phylogenetic lineages previously defined by multilocus sequence typing, especially for the sequence type (ST) 17, which is considered hypervirulent. Among other idiosyncrasies, ST-17 shows a significantly lower number of spacers in comparison with other lineages. This characteristic could reflect the peculiar virulence or colonization specificities of this lineage.

Analysis of the Type II-A CRISPR-Cas System in <i>Streptococcus canis</i> Isolated from Diseased Companion Animals and One Human Patient in Japan

“…urv.cat UPGMA index.php), and a phylogenetic dendrogram was constructed using NJplot (http: doua.prabi.fr software njplot). The spacers' structure and polymorphisms were illustrated using graphic representation as previously described (2,3). We constructed a tree showing different SCM allele types.…”

“…Indeed, CRISPR-Cas systems are used as a beneficial tool to predict ancestral genotypes and descent patterns within microbial groups (2). Lier et al (3) reported that analysis of the type II-A CRISPR-Cas system of Streptococcus agalactiae reveals distinctive characteristics according to genetic lineages because the type II-A system is ubiquitous, whereas the type I-C system is present in approximately 20 of the strains.…”

Conserved DNA motifs in the type II-A CRISPR leader region

“…It was concluded that sequences at the leader-repeat junction recruits the adaptation machinery to this region for integration of new spacers (Wei et al, 2015). In a recent study that analyzed the spacer variation in 126 human isolates of S. agalactiae , the 3′ leader end of most of the isolates had a TACGAG sequence (Lier et al, 2015). Our analysis that focused on many divergent genera uncovered that the DNA motifs that were previously known to be important for streptococcal adaptation is in fact more ubiquitous and conserved across different bacteria.…”

cas9 Enhances Bacterial Virulence by Repressing the regR Transcriptional Regulator in Streptococcus agalactiae

“…By analysis of the S. agalactiae strains that have been sequenced to date, two different CRISPR-Cas systems were found in S. agalactiae strains: the type II-A system is ubiquitous and the type I-C system is present in only 20% of isolated strains (20,21). Although the existence of these two systems has been clearly demonstrated, their function and impact on the virulence of S. agalactiae are still unknown.…”