Control of Virulence by the Two-Component System CiaR/H Is Mediated via HtrA, a Major Virulence Factor ofStreptococcus pneumoniae

Abstract

The CiaR/H two-component system is involved in regulating virulence and competence in Streptococcus pneumoniae. The system is known to regulate many genes, including that for high-temperature requirement A (HtrA). This gene has been implicated in the ability of the pneumococcus to colonize the nasopharynx of infant rats. We reported previously that deletion of the gene for HtrA made the pneumococcal strains much less virulent in mouse models, less able to grow at higher temperatures, and more sensitive to oxidative stress. In this report, we show that the growth phenotype as well as sensitivity to oxidative stress of ⌬ciaR mutant was very similar to that of a ⌬htrA mutant and that the expression of the HtrA protein was reduced in a ciaR-null mutant. Both the in vitro phenotype and the reduced virulence of ⌬ciaR mutant could be restored by increasing the expression of HtrA.Streptococcus pneumoniae (the pneumococcus) is an important human pathogen. This gram-positive organism is a major cause of a variety of diseases such as pneumonia, bacteremia, meningitis, otitis media, and sinusitis in both adults and children all over the world (40,43). The nasopharynx is the major reservoir of pneumococci, from which they can spread to other sites such as bloodstream or lung tissues (44).Pathogenic bacteria encounter a number of environmental stresses during their life cycle such as temperature shifts, variations in osmolarity, changes in pH, and nutrient deprivation (45). The pneumococcus responds to these stresses, particularly heat stress, by mediating a cascade of events leading to the synthesis of a unique group of proteins called heat shock proteins (HSPs) (7). The production of these proteins represents a protective cellular response to cope with the stressinduced damage of proteins (26). HSPs are molecular chaperones or proteases that take part in protein quality control during normal growth and under stress-inducing conditions (6,12).Recent studies have demonstrated the role of bacterial twocomponent signal-transducing systems in mediating adaptive responses to environmental signals (30, 38). The pneumococcal CiaR/H two-component system consists of a sensor histidine kinase, CiaH, anchored in the cell membrane and a cytoplasmic response regulator, CiaR, which is a DNA-binding protein involved in the regulation of genes in response to environmental signals sensed by CiaH (15). This system was identified as 1 of 13 two-component signal-transducing systems in two genomic screens (24, 42). Pleotropic effects caused by cia mutations in the pneumococcus include sensitivity to cefotaxime, an ability to form protoplast, susceptibility to lysis by deoxycholate (11), and a tendency to early lysis (24). CiaH mutants also have transformation deficiency (8,11,16). In vivo, CiaR/H has been shown to contribute to colonization of the mouse lung (42) and the nasopharynx of infant rats (35) and to be involved in systemic infection in mice (27). Previous studies have shown that the CiaR/H regulon contains many genes, including the hig...

Regulation of Gene Expression inStreptococcus pneumoniaeby Response Regulator 09 Is Strain Dependent

“…3b; see Tables S1 to S3 in the supplemental material). These genes include a putative operon (sp2141 to sp2144) predicted to be involved in N-glycan degradation and the serine protease htrA gene (10,11,25), which are downregulated at an OD 600 of 0.6 in BHI broth.…”

The CiaRH System ofStreptococcus pneumoniaePrevents Lysis during Stress Induced by Treatment with Cell Wall Inhibitors and by Mutations inpbp2xInvolved in β-Lactam Resistance

“…In addition to the initial observations that mutations in the histidine kinase CiaH cause changes in susceptibility to cefotaxime and interfere with genetic competence (14), the CiaRH system contributes to autolysis in complex media (6,10,18,30,36), DOCmediated lysis (10), and thermotolerance and oxidative stress tolerance (8,22) and affects pneumococcal virulence in vivo in mouse infection models (34,44,48). The present analysis has extended cia-mediated effects to a whole battery of conditions that are related to cellular lysis: inhibition of early and late stages of peptidoglycan biosynthesis by antibiotics and prevention of teichoic acid biosynthesis by depletion of choline in the growth medium.…”

“…The CiaRH system is an important virulence factor in systemic infections in mice and contributes to colonization of the mouse lung and the nasopharynx of infant rats (34,44,48). One of the genes controlled by CiaR, the protease/chaperone HtrA, has recently been analyzed in detail and appears to be the main mediator of the virulence phenotype and competence inhibition of cia mutants (21,22,44,45). Furthermore, increased autolysis of ciaR mutant cells has been observed under many conditions, including stationary-phase lysis and lysis triggered by deoxycholate or upon addition of CSP (6,10,18,30).…”

The NLRP3 Inflammasome Is Differentially Activated by Pneumolysin Variants and Contributes to Host Defense in Pneumococcal Pneumonia

“…The altered gene was then introduced into the chromosome as described above using Janus mutagenesis. Full-length or truncation variants of PLY were constructed by transformation with the shuttle vector pALYI (37) containing the appropriate DNA insert. Hemolytic assay was performed as described previously (38).…”