Phenotypic and Transcriptional Characterization of the Meningococcal PhoPQ System, a Magnesium-Sensing Two-Component Regulatory System That Controls Genes Involved in Remodeling the Meningococcal Cell Surface

Abstract

We previously identified and characterized a two-component regulatory system in the meningococcus with homology to the phoP-phoQ system in salmonella and showed that allele replacement of the NMB0595 regulator gene led to loss of virulence, sensitivity to antimicrobial peptides, perturbed protein expression, and magnesium-sensitive growth. On the basis of these findings we proposed that the system should be designated the meningococcal PhoPQ system. Here we further characterized the NMB0595 mutant and demonstrated that it had increased membrane permeability and was unable to form colonies on solid media with low magnesium concentrations, features that are consistent with disruption of PhoPQ-mediated modifications to the lipooligosaccharide structure. We examined the transcriptional profiles of wild-type and NMB0595 mutant strains and found that magnesium-regulated changes in gene expression are completely abrogated in the mutant, indicating that, similar to the salmonella PhoPQ system, the meningococcal PhoPQ system is regulated by magnesium. Transcriptional profiling of the mutant indicated that, also similar to the salmonella PhoPQ system, the meningococcal system is involved in control of virulence and remodeling of the bacterial cell surface in response to the host environment. The results are consistent with the hypothesis that the PhoP homologue plays a role in the meningococcus similar to the role played by PhoP in salmonella. Elucidating the role that the PhoPQ system and PhoPQ-regulated genes play in the response of the meningococcus to the host environment may provide new insights into the pathogenic process.

A two-component system is required for colonization of host cells by meningococcus

“…Two independent transcriptomic analyses reported lists of genes whose expression was altered in meningococcal strains inactivated for the NMA0798 gene (Newcombe et al, 2005;Tzeng et al, 2008). Only 29 genes were identified in both studies and among them none of the REP2 genes.…”

“…Newcombe et al (2005) renamed the NMA0797/0798 TCS PhoP/PhoQ based on similar phenotypes of the two TCSs in response to Mg 2+ . However, the transcriptomic analysis that the authors performed did not identify any gene involved in the transport of Mg 2+ as being transcriptionally altered in a NMA0798 background.…”

“…This TCS was also shown to be necessary for the bacterium to cross an epithelial cell layer (Johnson et al, 2001), and was demonstrated to constitute a functional signal transduction system (Tzeng et al, 2006) that modulates the meningococcal virulence factor lipopolysaccharide (Tzeng et al, 2004). In addition, transcriptomic analyses revealed that inactivation of NMA0798 perturbed the expression of a large number of genes (Newcombe et al, 2005), many of which are involved in the synthesis of components of the meningococcal cell surface (Tzeng et al, 2008).…”

“…Experimental evidence demonstrating a regulatory function is only available for one of these four TCSs, i.e. the NMA0797 (PhoQ, MisS)/0798 (PhoP, MisR) system (Johnson et al, 2001;Newcombe et al, 2004Newcombe et al, , 2005Tzeng et al, 2004Tzeng et al, , 2006Tzeng et al, , 2008. A meningococcal knockout mutant in the NMA0798 gene was reported to display an attenuated virulence phenotype in a mouse model of infection (Newcombe et al, 2004).…”

Post-genomics ofNeisseria meningitidis: an update

“…Between 2005 and 2008, many studies employed transcriptome analysis for the characterization of diverse aspects of N. meningitidis physiology, in particular regulation by the two-component signal transduction NMB0595/NMB0594 [22,23] and iron availability [24,25], as well as the host cell response to a live bacterial infection [26][27][28][29][30].…”