Microarray-Based Identification of htrA , a Streptococcus pneumoniae Gene That Is Regulated by the CiaRH Two-Component System and Contributes to Nasopharyngeal Colonization

Abstract

Nasopharyngeal carriage is the reservoir from which most disease with Streptococcus pneumoniae arises. Survival as a commensal in this environment is likely to require a set of adaptations distinct from those needed to cause disease, some of which may be mediated by two-component signal transduction systems (TCSTS). We examined the contributions of nine pneumococcal TCSTS to the process of nasopharyngeal colonization by using an infant rat model. Whereas deletions in all but one of these systems have been associated previously with a high degree of attenuation in a murine model of pneumonia, only the CiaRH system was necessary for efficient carriage. Transcriptional analysis by using microarray hybridization identified a locus consisting of two adjacent genes, htrA and spoJ, that was specifically and strongly downregulated in a ⌬ciaRH-null mutant. A S. pneumoniae strain lacking the htrA gene encoding a putative serine protease, but not one lacking spoJ, showed decreased fitness in a competitive model of colonization, a finding consistent with this gene mediating a portion of the carriage deficit observed with the ⌬ciaRH strain.Streptococcus pneumoniae exists in nature both as a commensal on the mucosal surface of the human upper respiratory tract and as a pathogen causing disease in a wide range of sites, including the lung, middle ear, sinuses, blood, and meninges. Survival in these different host environments is likely to require adaptive responses, some of which may be mediated by twocomponent signal transduction systems (TCSTS). These signaling systems (reviewed in reference 27) are found in a wide range of bacteria where they have been shown to regulate diverse processes, including chemotaxis, nutrient utilization, surface adhesion, and the switch between aerobic and anaerobic metabolism. TCSTS consist of a sensor kinase that autophosphorylates in response to an environmental stimulus and a cognate response regulator to which an activated phosphate is transferred and that then mediates a downstream response, often acting as a DNA-binding protein to cause changes in gene expression.Two genomic surveys of S. pneumoniae have identified 13 pairs of genes encoding putative TCSTS as well as a single unpaired putative response regulator (12, 29). The ability of null mutants in these systems to cause disease has been previously examined in two studies of virulence. In a murine model of pneumonia developing after intranasal inoculation in which all of the TCSTS except ComDE were tested, deletions in eight of the systems resulted in an attenuation of at least 3 orders of magnitude (29). In contrast, a second study testing a collection of single-crossover mutants in a different genetic background showed no evidence of decreased virulence for any of the strains in a murine model of intraperitoneal infection in which the requirements of adaptation to the mucosal surface of the airway were circumvented (12). Despite the importance of nasal carriage both as the first step in the pathogenesis of pneumococcal disease and in...

The HtrA Protease from Streptococcus pneumoniae Digests Both Denatured Proteins and the Competence-stimulating Peptide

“…Considering that positive feedback strongly amplifies the production of CSP once competence has begun, the reduced efficacy of HtrA in turning competence off as opposed to blocking its initiation may be the result of higher pheromone levels at the later stage. Finally, it is important to note that although HtrA expression is regulated by at least two signaling systems (10,43), changes in HtrA levels are not responsible for the modulation of competence by this protease that allows it to serve as a sensor for the accuracy of protein biosynthesis (Fig. 6, G and H) (8).…”

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

“…Microarray-based transcription analyses showed that the entire competence regulon including the comCDE operon was turned off in the R6ciaH C306 strain, whereas loss-of-function CiaR mutants were perfectly competent under growth conditions that prevented competence development in the wild type (36,44). On the other hand, the CiaR regulon was shown to be induced during competence within the group of "delayed" competence genes, i.e., it is itself regulated indirectly by the ComDE system (41), and evidence was presented that the CiaRH system might be required for the cells to exit normally from the competent state (6).…”

“…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).…”

“…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 two-component signal transduction system RR06/HK06 regulates expression of cbpA in Streptococcus pneumoniae

“…The best characterized of these is ComDE, which activates the genetic competence system in response to a competence-stimulating peptide (6,7). Another system, CiaRH, also affects competence and has been shown to control a novel virulence factor, HtrA (8,9). More recently, HK͞RR04 has been linked to the control of the Mn transporter PsaA, although this regulation was apparently strainspecific (10).…”