Li Jihong, Wu Zhihao, Wu Changsong, Chen Dan-Dan, Zhou Yang, Zhang Yong-An
Institute of Hydrobiology, Chinese Academy of Sciences (CAS), Wuhan, China.
University of Chinese Academy of Sciences, Beijing, China.
Front Vet Sci. 2021 Dec 13;8:793458. doi: 10.3389/fvets.2021.793458. eCollection 2021.
is a Gram-negative bacterium that is commonly distributed in aquatic surroundings and has been considered as a pathogen of fish, amphibians, reptiles, and mammals. In this study, a virulent strain GD18, isolated from grass carp (), was characterized to belong to a new sequence type ST656. Whole-genome sequencing and phylogenetic analysis showed that GD18 was closer to environmental isolates, however distantly away from the epidemic ST251 clonal group. The type VI secretion system (T6SS) was known to target both eukaryotic and prokaryotic cells by delivering various effector proteins in diverse niches by Gram-negative bacteria. Genome-wide searching and hemolysin co-regulated protein (Hcp) expression test showed that GD18 possessed a functional T6SS and is conditionally regulated. Further analysis revealed that VasH, a σ54-transcriptional activator, was strictly required for the functionality of T6SS in GD18. Mutation of H gene by homologous recombination significantly abolished the bactericidal property. Then the virulence contribution of VasH was characterized in both and models. The results supported that VasH not only contributed to the bacterial cytotoxicity and resistance against host immune cleaning, but also was required for virulence and systemic dissemination of GD18. Taken together, these findings provide a perspective for understanding the VasH-mediated regulation mechanism and T6SS-mediated virulence and bactericidal effect of .
是一种革兰氏阴性菌，广泛分布于水生环境中，被认为是鱼类、两栖动物、爬行动物和哺乳动物的病原体。在本研究中，从草鱼中分离出的一株强毒株GD18，经鉴定属于一种新的序列类型ST656。全基因组测序和系统发育分析表明，GD18与环境分离株更为接近，但与流行的ST251克隆群距离较远。已知VI型分泌系统（T6SS）通过革兰氏阴性菌在不同生态位传递各种效应蛋白来靶向真核细胞和原核细胞。全基因组搜索和溶血素共调节蛋白（Hcp）表达测试表明，GD18拥有功能性T6SS且受条件调节。进一步分析表明，σ54转录激活因子VasH是GD18中T6SS功能所必需的。通过同源重组对H基因进行突变显著消除了杀菌特性。然后在和模型中对VasH的毒力贡献进行了表征。结果支持VasH不仅有助于细菌的细胞毒性和对宿主免疫清除的抗性，而且是GD18毒力和全身传播所必需的。综上所述，这些发现为理解VasH介导的调节机制以及GD18的T6SS介导的毒力和杀菌作用提供了一个视角。
