Gao He, Zhang Jingyun, Lou Jing, Li Jie, Qin Qin, Shi Qiannan, Zhang Yiquan, Kan Biao
State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China.
School of Medicine, Jiangsu University, Zhenjiang, China.
Front Microbiol. 2020 Apr 17;11:709. doi: 10.3389/fmicb.2020.00709. eCollection 2020.
Cholera toxin (CT) and toxin coregulated pilus (TCP, TcpA is the major subunit) are two major virulence factors of , both of which play critical roles in developing severe diarrhea in human. Expression of CT and TCP is under the tight control of the regulatory cascade known as the ToxR virulence regulon, which is composed of three regulators ToxR, TcpP, and ToxT. Besides, their expression is also regulated by the quorum sensing (QS) master regulator HapR and the regulatory protein Fur. Though transcription of , , and/or are reported to be regulated by HapR and Fur, to date there are no studies to verify their direct regulations. In the present study, we showed that HapR directly repress the transcription of and by binding to their promoter regions, and possibly repress transcription in an indirect manner. Fur directly activated the transcription of , , and by binding to their promoters. Taking account of the sequential expression of , , , , and in the different growth phases of , we deduce that at the early mid-logarithmic growth phase, Fur binds to the promoters of , , and to activate their transcription; while at the later mid-logarithmic growth phase, HapR can bind to the promoters of and to repress their transcription. Our study reveals the new recognition in the virulence regulatory pathways in and suggests the complicated and subtle regulation network with the growth density dependence.
霍乱毒素（CT）和毒素共调节菌毛（TCP，TcpA是主要亚基）是霍乱弧菌的两个主要毒力因子，二者在导致人类严重腹泻过程中均发挥关键作用。CT和TCP的表达受到一种名为ToxR毒力调节子的调控级联的严格控制，该调节子由ToxR、TcpP和ToxT三种调节因子组成。此外，它们的表达还受群体感应（QS）主调节因子HapR和调节蛋白Fur的调控。尽管据报道霍乱弧菌、CT和/或TCP的转录受HapR和Fur调控，但迄今为止尚无研究验证它们的直接调控作用。在本研究中，我们发现HapR通过结合霍乱弧菌、CT和TCP的启动子区域直接抑制它们的转录，并且可能以间接方式抑制TCP的转录。Fur通过结合霍乱弧菌、CT和TCP的启动子直接激活它们的转录。考虑到霍乱弧菌在不同生长阶段霍乱弧菌、CT、TCP、ToxR和TcpP的顺序表达，我们推断在对数生长中期早期，Fur结合霍乱弧菌、CT和TCP的启动子以激活它们的转录；而在对数生长中期后期，HapR可结合霍乱弧菌和CT的启动子以抑制它们的转录。我们的研究揭示了霍乱弧菌毒力调控途径中的新认识，并提示了具有生长密度依赖性的复杂而微妙的调控网络。
