A MARTX Toxin Gene Is Controlled by Host Environmental Signals through a CRP-Coordinated Regulatory Network in Vibrio vulnificus.

A multifunctional autoprocessing repeats-in-toxin (MARTX) toxin plays an essential role in the virulence of many pathogens, including a fulminating human pathogen H-NS and HlyU repress and derepress expression of the MARTX toxin gene in , respectively. However, little is known about other regulatory proteins and environmental signals involved in regulation. In this study, we found that a leucine-responsive regulatory protein (Lrp) activates by binding directly and specifically to the promoter, P Phased hypersensitivity resulting from DNase I cleavage of the P regulatory region suggests that Lrp probably induces DNA bending in P Lrp activates P independently of H-NS and HlyU, and leucine inhibits Lrp binding to P and reduces the Lrp-mediated activation. Furthermore, a cyclic AMP receptor protein (CRP) represses P , and exogenous glucose relieves the CRP-mediated repression. Biochemical and mutational analyses demonstrated that CRP binds directly and specifically to the upstream region of P , which presumably alters the DNA conformation in P and thus represses Moreover, CRP represses expression of and by binding directly to their upstream regions, forming coherent feed-forward loops with Lrp and HlyU. In conclusion, expression of is controlled by a regulatory network comprising CRP, Lrp, H-NS, and HlyU in response to changes in host environmental signals such as leucine and glucose. This collaborative regulation enables the elaborate expression of , thereby enhancing the fitness and pathogenesis of during the course of infection. A MARTX toxin, RtxA, is an essential virulence factor of many pathogens, including species. H-NS and HlyU repress and derepress, respectively, expression of a life-threatening pathogen, We found that Lrp directly activates independently of H-NS and HlyU, and leucine inhibits the Lrp-mediated activation of Furthermore, we demonstrated that CRP represses but derepresses in the presence of exogenous glucose. CRP represses not only directly by binding to upstream of but also indirectly by repressing and This is the first report of a regulatory network comprising CRP, Lrp, H-NS, and HlyU, which coordinates the expression in response to environmental signals such as leucine and glucose during infection. This elaborate regulatory network will enhance the fitness of and contribute to its successful infection within the host.