Section of Microbiology, University of Copenhagen, Copenhagen, Denmark.
Department of Microbiology and Immunology, University of California, San Francisco, CA, USA.
Nat Commun. 2020 Nov 6;11(1):5652. doi: 10.1038/s41467-020-19415-3.
Many prokaryotes employ CRISPR-Cas systems to combat invading mobile genetic elements (MGEs). In response, some MGEs have developed strategies to bypass immunity, including anti-CRISPR (Acr) proteins; yet the diversity, distribution and spectrum of activity of this immune evasion strategy remain largely unknown. Here, we report the discovery of new Acrs by assaying candidate genes adjacent to a conserved Acr-associated (Aca) gene, aca5, against a panel of six type I systems: I-F (Pseudomonas, Pectobacterium, and Serratia), I-E (Pseudomonas and Serratia), and I-C (Pseudomonas). We uncover 11 type I-F and/or I-E anti-CRISPR genes encoded on chromosomal and extrachromosomal MGEs within Enterobacteriaceae and Pseudomonas, and an additional Aca (aca9). The acr genes not only associate with other acr genes, but also with genes encoding inhibitors of distinct bacterial defense systems. Thus, our findings highlight the potential exploitation of acr loci neighborhoods for the identification of previously undescribed anti-defense systems.
许多原核生物利用 CRISPR-Cas 系统来对抗入侵的移动遗传元件（MGE）。作为回应，一些 MGE 已经开发出了绕过免疫的策略，包括抗 CRISPR（Acr）蛋白；然而，这种免疫逃避策略的多样性、分布和活性范围在很大程度上仍然未知。在这里，我们通过针对一组六个 I 型系统（I-F（假单胞菌、果胶杆菌和沙雷氏菌）、I-E（假单胞菌和沙雷氏菌）和 I-C（假单胞菌）），检测保守 Acr 相关（Aca）基因 aca5 附近的候选基因，发现了新的 Acr。我们在肠杆菌科和假单胞菌的染色体和染色体外 MGE 中发现了 11 个编码 I-F 和/或 I-E 抗 CRISPR 基因，以及一个额外的 Aca（aca9）。acr 基因不仅与其他 acr 基因相关，还与编码不同细菌防御系统抑制剂的基因相关。因此，我们的发现强调了利用 acr 基因座周围的区域来鉴定以前未描述的抗防御系统的潜力。
