Streptococcus mutans and its virulent phages are important members of the human oral microbiota. S. mutans is also the primary causal agent of dental caries. To survive in this ecological niche, S. mutans must encode phage defense mechanisms, which include CRISPR-Cas systems. Here, we describe the CRISPR-Cas type II-A system of S. mutans strain P42S, which was found to display natural adaptation and interference activity in response to phage infection and plasmid transformation. Newly acquired spacers were integrated both at the 5′ end of the CRISPR locus and ectopically. In comparisons of the cas genes of P42S to those of other strains of S. mutans, cas1, cas2, and csn2 appear to be highly conserved within the species. However, more diversity was observed with cas9. While the nuclease domains of S. mutans Cas9 (SmCas9) are conserved, the C terminus of the protein, including the protospacer adjacent motif (PAM) recognition domain, is less conserved. In support of these findings, we experimentally demonstrated that the PAMs associated with SmCas9 of strain P42S are NAA and NGAA. These PAMs are different from those previously reported for the CRISPR-Cas system of the model strain S. mutans UA159. This study illustrates the diversity of CRISPR-Cas type II-A systems that can be found within the same bacterial species.

中文翻译：

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变形链球菌中II-A型CRISPR-Cas系统的表征。

变形链球菌及其毒性噬菌体是人类口腔微生物群的重要成员。变形链球菌也是龋齿的主要病因。为了在这种生态环境中生存，变形链球菌必须编码噬菌体防御机制，其中包括CRISPR-Cas系统。在这里，我们描述了变形链球菌菌株P42S的CRISPR-Cas II-A型系统，发现该系统显示出对噬菌体感染和质粒转化的自然适应性和干扰活性。新获得的间隔子在CRISPR基因座的5'端和异位整合。在的比较CAS那些的其它菌株的P42S的基因变异链球菌，CAS1，cas2和csn2似乎在该物种内高度保守。但是，使用cas9可以观察到更多的多样性。尽管变形链球菌Cas9的核酸酶结构域（SmCas9）是保守的，但蛋白质的C末端（包括原间隔子相邻基序（PAM）识别域）却不太保守。为了支持这些发现，我们实验证明了与P42S菌株SmCas9相关的PAM是NAA和NGAA。这些PAM与先前针对变形链球菌UA159的CRISPR-Cas系统报道的PAM不同。这项研究说明了可以在同一细菌物种中发现的CRISPR-Cas II-A型系统的多样性。