YhjC is a novel transcriptional regulator required for Shigella flexneri virulence

Shigella is an intracellular pathogen that primarily infects the human colon and causes shigellosis. Shigella virulence relies largely on the type III secretion system (T3SS) and secreted effectors. VirF, the master Shigella virulence regulator, is essential for the expression of T3SS-related genes. In this study, we found that YhjC, a LysR-type transcriptional regulator, is required for Shigella virulence through activating the transcription of virF. Pathogenicity of the yhjC mutant, including colonization in the colons of guinea pigs as well as its ability for host cell adhesion and invasion, was significantly lowered. Expression levels of virF and nearly all VirF-dependent genes were downregulated by yhjC deletion, indicating that YhjC can activate virF transcription. Electrophoretic mobility shift assay analysis demonstrated that YhjC could bind directly to the virF promoter region. Therefore, YhjC is a novel virulence regulator that positively regulates the virF expression and promotes Shigella virulence. Additionally, genome-wide expression analysis identified the presence of other genes in the large virulence plasmid and a genome exhibiting differential expression in response to yhjC deletion, with 169 downregulated and 99 upregulated genes, indicating that YhjC also functioned as a global regulatory factor.

志贺氏菌（Shigella）是一类主要侵染人类结肠并引发志贺菌病的胞内致病菌。志贺氏菌的毒力主要依赖于Ⅲ型分泌系统（type III secretion system, T3SS）及其分泌的效应蛋白。VirF作为志贺氏菌的核心毒力调控因子，对Ⅲ型分泌系统相关基因的表达至关重要。本研究发现，LysR型转录调控因子YhjC可通过激活virF基因的转录，是志贺氏菌毒力所必需的。yhjC基因缺失突变株的致病力显著降低，其在豚鼠结肠内的定植能力以及宿主细胞黏附与侵袭能力均受到明显抑制。yhjC基因缺失会下调virF基因以及几乎所有VirF依赖型基因的表达水平，表明YhjC可直接激活virF的转录。电泳迁移率变动分析结果证实，YhjC能够直接结合virF基因的启动子区域。综上，YhjC是一种全新的毒力调控因子，可正向调控virF的表达并促进志贺氏菌的毒力。此外，全基因组表达分析显示，在yhjC基因缺失后，菌株的大毒力质粒及基因组上存在差异表达基因：其中169个基因表达下调，99个基因表达上调，这表明YhjC同时作为全局调控因子发挥功能。