Department of Epidemiology, College of Public Health, Zhengzhou University, Zhengzhou, People's Republic of China.
Arch Microbiol. 2021 Aug;203(6):3235-3243. doi: 10.1007/s00203-021-02310-w. Epub 2021 Apr 9.
The CRISPR-Cas system is widely distributed in prokaryotes and plays an important role in the adaptive immunity of bacteria and archaea. Bifidobacterium is an important component of the intestinal flora of humans and animals, and some species of this bacterium can be employed as food additives. However, the Bifidobacterium CRISPR-Cas system has not been fully elucidated to date. In this study, the genomes of 110 strains of Bifidobacterium were employed to research the diversity of the type I-U system. The 110 strains were divided into five groups according to the genes adjacent to the CRISPR locus, including group A, B, C, D and E. Strains in the intergroup had unique species classifications and MLST types. An evolutionary tree was constructed based on the conserved cas4/cas1 fusion gene. The results showed that group A had a different evolutionary branch compared with the other groups and had a relatively low spacer number. Notably, group B, C and E had exhibited ABC transporter regulators in the genes adjacent to the CRISPR locus. ABC transporters play important roles in the exocytosis of many antibiotics and are involved in horizontal gene transfer. This mechanism may have promoted the evolution of Bifidobacterium and the horizontal gene transfer of the type I-U system, which may have promoted the generation of system diversity. In summary, our results help to elucidate the role of the type I-U system in the evolution of Bifidobacterium.
CRISPR-Cas 系统广泛分布于原核生物中，在细菌和古菌的适应性免疫中发挥着重要作用。双歧杆菌是人和动物肠道菌群的重要组成部分，该细菌的一些种可作为食品添加剂。然而，双歧杆菌的 CRISPR-Cas 系统尚未得到充分阐明。在本研究中，利用 110 株双歧杆菌的基因组研究了 I-U 型系统的多样性。根据 CRISPR 基因座附近的基因，将 110 株菌分为 A、B、C、D 和 E 五组。组间菌株具有独特的物种分类和 MLST 型。根据保守的 cas4/cas1 融合基因构建了进化树。结果表明，A 组与其他组相比具有不同的进化分支，间隔区数量相对较少。值得注意的是，B、C 和 E 组在 CRISPR 基因座附近的基因中表现出 ABC 转运体调节剂。ABC 转运体在许多抗生素的外排中发挥重要作用，并且参与水平基因转移。这种机制可能促进了双歧杆菌的进化和 I-U 型系统的水平基因转移，从而促进了系统多样性的产生。总之，我们的研究结果有助于阐明 I-U 型系统在双歧杆菌进化中的作用。
