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Regulation of gene expression in Streptococcus pneumoniae by response regulator 09 is Strain-Dependent

ABSTRACT: Recent murine studies have demonstrated that the role of response regulator 09 (RR09) of S. pneumoniae in virulence varies between strains. In the present study, we used a murine pneumonia model of infection to assess the virulence of a TIGR4 rr09-mutant, and found that TIGR4Δrr09 was attenuated after intranasal infection. Further, we investigated the in vitro transcriptional changes in pneumococcal rr09 mutants of two strains, D39 and TIGR4, by microarray analysis. The transcriptional profiles of the rr09 mutants in both strains displayed clear differences compared to their parental wild-type. In D39Δrr09 but not TIGR4Δrr09, genes involved in competence (e.g. comAB) were upregulated. In TIGR4, genes located on the rlrA pathogenicity islet, absent in the D39 genome, appeared to be regulated by RR09. Furthermore, several phosphotransferase systems (PTSs), believed to be involved in sugar uptake (e.g., sp0060-sp0066), were strongly downregulated in D39Δrr09, while not regulated by RR09 in TIGR4. To address the role of one of these PTS in virulence, D39Δsp0063 was constructed and tested in a murine infection model. No difference in virulence compared to the wild-type was found, indicating that downregulation of this gene alone is not the cause of the avirulent phenotype of D39Δrr09. Finally, expression of rr09 and three of our identified RR09 targets were assessed during infection in mice. This in vivo experiment confirmed differences in expression between TIGR4 wild-type and rr09-mutant, as well as between wild-type D39 and TIGR4. In conclusion, our results indicate strain-specific regulation of pneumococcal gene expression by RR09. Keywords: genetic modification

ORGANISM(S): Streptococcus pneumoniae

PROVIDER: GSE6137 | GEO | 2006/12/24

SECONDARY ACCESSION(S): PRJNA97701

REPOSITORIES: GEO

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Project description:Infection of the human host by Streptococcus pneumoniae begins with colonization of the nasopharynx, which is mediated by adherence of bacteria to respiratory epithelium. Several studies have indicated an important role for the pneumococcal capsule in this process. Here, we used microarrays to characterize the in vitro transcriptional response of human nasopharyngeal epithelial Detroit 562 cells to adherence of serotype 2-encapsulated strain D39, serotype 19F-encapsulated strain G54, serotype 4-encapsulated strain TIGR4, and their nonencapsulated derivatives (delta-cps). In total, 322 genes were found to be upregulated in response to adherent pneumococci. Twenty-two genes were commonly induced, including those encoding several cytokines (e.g., IL-1-beta, IL-6), chemokines (e.g., IL-8, CXCL1/2), and transcriptional regulators (e.g., FOS), consistent with an innate immune response mediated by Toll-like receptor signaling. Interestingly, 85% of genes was induced specifically by one or more encapsulated strains, suggestive of a capsule-dependent response. Importantly, purified capsular polysaccharides alone had no effect. Over a third of these loci encoded products predicted to be involved in transcriptional regulation and signal transduction, in particular MAPK signaling pathways. Real-time PCR of a subset of ten genes confirmed microarray data and showed a time-dependent upregulation of especially innate immunity genes. Downregulation of epithelial genes was most pronounced upon adherent D39delta-cps, as 68% of the 161 genes identified was only repressed using this nonencapsulated strain. In conclusion, we identified a subset of host genes specifically induced by encapsulated strains during in vitro adherence, and have demonstrated the complexity of interactions occurring during the initial stages of pneumococcal infection. Experiment Overall Design: We used three different pneumococcal strains and their isogenic nonencapsulated derivatives (delta-cps): serotype 2-encapsulated strain D39, serotype 19F-encapsulated strain G54, and serotype 4-encapsulated strain TIGR4. All experiments were performed in triplicate (3 independent biological replicates) and compared to uninfected control Detroit 562 cells. Bacteria were allowed to adhere to the epithelial cells for 2 hours, after which the transcriptional response of the Detroit cells was analyzed using Affymetrix Human U133 Plus GeneChips. In addition to the 6 strains mentioned above, we included transcriptional analysis of the epithelial cell response to low-dose D39delta-cps (giving adherence equivalent to wild-type D39) and purified type 2 capsular polysaccharides.

Project description:Previous studies have indicated that PsaR of Streptococcus pneumoniae is a manganese-dependent regulator, negatively affecting the expression of at least seven genes. Here, we extended these observations by transcriptome and proteome analysis of psaR mutants in strains D39 and TIGR4. The microarray analysis identified three shared PsaR targets: the psa-operon, pcpA, and prtA. Additionally, we found 31 genes to be regulated by PsaR in D39 only, most strikingly a cellobiose-specific PTS and a putative bacteriocin operon (sp0141-sp0146). In TIGR4, 14 PsaR gene targets were detected, with the rlrA pathogenicity islet being the most pronounced. Proteomics confirmed most of the shared gene targets. To examine the contribution of PsaR to pneumococcal virulence, we compared D39 and TIGR4 wild-type (wt) and psaR-mutants in three murine infection models. During colonization, no clear effect was observed of the psaR mutation in either D39 or TIGR4. In the pneumonia model, small but significant differences were observed in the lungs of mice infected with either D39wt or âpsaR: D39âpsaR had an initial advantage in survival in the lungs. Conversely, TIGR4âpsaR-infected mice had significantly lower bacterial loads at 24h only. Finally, during experimental bacteremia, D39âpsaR-infected mice had significantly lower bacterial loads in the blood stream than wt-infected mice for the first 24h of infection. TIGR4âpsaR showed attenuation at 36h only. In conclusion, our results show that PsaR of D39 and TIGR4 has a strain-specific role in global gene expression and in the development of bacteremia in mice. Microarray analysis was performed essentially as described (Hendriksen et al., 2007; Hendriksen et al., 2008a). In short, 500 ml of CDM was inoculated with 10-20 colonies from agar plates, and these cultures were statically grown at 37Â°C. Samples for RNA isolation were taken when the cultures reached an optical density (OD600) of 0.2 (mid-log growth). RNA was isolated and purified using the High Pure RNA isolation kit (Roche diagnostics) as described (Hendriksen et al., 2007; Hendriksen et al., 2008a). Contaminating genomic DNA was removed by treatment with RNase-free DNase I (Roche diagnostics). RNA was isolated from three replicate cultures. Synthesis, subsequent labeling of cDNA, and microarray hybridization was performed as described (Hendriksen et al., 2007; Kloosterman et al., 2006). In all cases, dye-swapping was performed with one of the three biological replicates. Microarrays used in this study were constructed as described (Hendriksen et al., 2007; Kloosterman et al., 2006) and contain amplicons representing 2,087 ORFs of S. pneumoniae TIGR4 and 184 ORFs unique for S. pneumoniae R6, all spotted in duplicate.

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Regulation of gene expression in Streptococcus pneumoniae by response regulator 09 is Strain-Dependent

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