The clustered regularly interspaced short palindromic repeats (CRISPRs) and their associated proteins (Cas) are immune systems in prokaryotes present in most Bacteria and Archaea. They provide adaptive immunity against foreign elements such as bacteriophages/viruses, plasmids and transposons. During immunization a small sequence of foreign DNA, a so-called spacer is integrated into the CRISPR locus in the host cell. Spacers are then transcribed into small RNA guides that direct cleavage of foreign DNA by Cas nucleases. Immunization through spacer acquisition is transferred vertically to the progeny. It is possible that this genetic immune system of bacteria participates in modulating the microbiome of ‘chronic’ periodontitis, in which Porphyromonas gingivalis has been identified as a keystone pathogen causing microbial dysbiosis. An in-depth review of our current knowledge on the CRISPR-Cas systems in P. gingivalis is given in this paper with the attempt to understand how this anaerobic bacterium may protect itself in the periodontal pocket where bacteriophages are abundant and even out-number bacteria.

成簇的规则间隔的短回文重复序列 (CRISPR) 及其相关蛋白 (Cas) 是存在于大多数细菌和古细菌中的原核生物的免疫系统。它们提供针对外来元素的适应性免疫，例如噬菌体/病毒、质粒和转座子。在免疫期间，一小段外源 DNA 被整合到宿主细胞的 CRISPR 基因座中。然后将间隔区转录成小 RNA 指导，指导 Cas 核酸酶切割外来 DNA。通过间隔物获得的免疫被垂直转移到后代。这种细菌的遗传免疫系统可能参与调节“慢性”牙周炎的微生物组，其中牙龈卟啉单胞菌已被确定为导致微生物生态失调的关键病原体。本文深入回顾了我们目前对牙龈卟啉单胞菌CRISPR-Cas 系统的了解，试图了解这种厌氧细菌如何在噬菌体丰富甚至数量超过细菌的牙周袋中保护自己.