Direct Binding and Regulation by Fur and HapR of the Intermediate Regulator and Virulence Factor Genes Within the ToxR Virulence Regulon in Vibrio cholerae

Abstract

Cholera toxin (CT) and toxin coregulated pilus (TCP, TcpA is the major subunit) are two major virulence factors of Vibrio cholerae, 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 tcpP, toxT, and/or tcpA 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 tcpP and tcpA by binding to their promoter regions, and possibly repress toxT transcription in an indirect manner. Fur directly activated the transcription of tcpP, toxT, and tcpA by binding to their promoters. Taking account of the sequential expression of hapR, fur, tcpP, toxT, and tcpA in the different growth phases of V. cholerae, we deduce that at the early midlogarithmic growth phase, Fur binds to the promoters of tcpP, toxT, and tcpA to activate their transcription; while at the later mid-logarithmic growth phase, HapR can bind to the promoters of tcpP and tcpA to repress their transcription. Our study reveals the new recognition in the virulence regulatory pathways in V. cholerae and suggests the complicated and subtle regulation network with the growth density dependence.

Vibrio splendidus Fur regulates virulence gene expression, swarming motility, and biofilm formation, affecting its pathogenicity in Apostichopus japonicus

“…Motility is an important virulence determinant during the adhesion and invasion stages in many pathogenic bacteria and enables bacterial cells to swim to nutrient-rich niches or avoid environmental stresses ( 46 ). Previous research has suggested that Fur directly activates the transcription of toxin coregulated pilus tcpA, which was necessary for colonization by binding to their promoters in V. cholerae ( 47 ). In Shigella flexneri , Fur could indirectly activate the icsA gene that facilitates bacterial movement by activating VirF ( 48 ).…”

Expression of Cholera Toxin (CT) and the Toxin Co-Regulated Pilus (TCP) by Variants of ToxT in Vibrio cholerae Strains

“…ToxT has been shown to directly bind to the promoters of virulence genes in V. cholerae [ 35 , 45 ]. The ToxT protein comprises 276 amino acids and belongs to the AraC/XylS-type transcriptional regulator family [ 13 , 46 , 47 ].…”

Vibrio cholerae senses human enteric α-defensin 5 through a CarSR two-component system to promote bacterial pathogenicity

“…Furthermore, a specific CarR-bound sequence (5-TAATGAGAATTACT-3; −186 to −172 from the tcpP translational start site) was confirmed. Previous research showed that several regulators could directly bind to the tcpP promoter, including AphA, AphB, HapR and CRP 47 , 48 . A small RNA (~91 nt), which was named TarA, is also located in the tcpP promoter 49 .…”