CsrRS Regulates Group BStreptococcusVirulence Gene Expression in Response to Environmental pH: a New Perspective on Vaccine Development

Abstract

To identify factors involved in the response of group B streptococci (GBS) to environmental pH, we performed a comparative global gene expression analysis of GBS at acidic and neutral pHs. We found that the transcription of 317 genes was increased at pH 5.5 relative to that at pH 7.0, while 61 genes were downregulated. The global response to acid stress included the differential expression of genes involved in transport, metabolism, stress response, and virulence. Known vaccine candidates, such as BibA and pilus components, were also regulated by pH. We observed that many of the genes involved in the GBS response to pH are known to be controlled by the CsrRS two-component system. Comparison of the regulon of wild-type strain 2603 V/R with that of a csrRS deletion mutant strain revealed that the pH-dependent regulation of 90% of the downregulated genes and 59.3% of the up-regulated genes in strain 2603 V/R was CsrRS dependent and that many virulence factors were overexpressed at high pH. Beta-hemolysin regulation was abrogated by selective inactivation of csrS, suggesting the implication of the CsrS protein in pH sensing. These results imply that the translocation of GBS from the acidic milieu of the vagina to the neutral pH of the neonatal lung signals the up-regulation of GBS virulence factors and conversion from a colonizing to an invasive phenotype. In addition, the fact that increased exposure of BibA on the bacterial surface at pH 7.0 induced opsonophagocytic killing of GBS in immune serum highlights the importance of pH regulation in the protective efficacy of specific antibodies to surface-exposed GBS proteins.

Regulation and Function of Pilus Island 1 in Group B Streptococcus

“…3E and F). An earlier study found that exposure of strain 2603 to pH 5.5 resulted in a 2-to 3-fold increase in ape1 expression as assessed in transcriptional profiling experiments using genomic microarrays (30). Increased expression of Ape1 could account for the observed upregulation of the PI-1 genes sag0645 and sag0647 at pH 5.0.…”

“…Unless otherwise specified, GBS was grown in Todd-Hewitt broth (THB; Difco) or on Trypticase soy agar (TSA) supplemented with 5% defibrinated sheep blood (PML Microbiologicals). For experiments testing the effects of pH, GBS was cultured at 37°C in complex medium (CM; 10 g/liter proteose peptone, 5 g/liter Trypticase peptone, 5 g/liter yeast extract, 2.5 g/liter KCl, 1 mM urea, 1 mM arginine) (30). E. coli was grown in Luria-Bertani broth, and L. lactis was grown in GM17 broth (M17 broth [Oxoid] supplemented with 0.5% glucose) (1).…”

Analysis of two-component sensor proteins involved in the response to acid stimuli in Streptococcus pyogenes

“…Dalton & Scott (2004) have reported that the growth of a CovS knockout mutant strain derived from M6 serotype strain JRS4 is impaired at low pH. In addition, Santi et al (2009) have reported that a CovRS homologue in Streptococcus agalactiae is involved in the pH-dependent regulation of gene expression. In this study, we did not identify a significant role for CovS but showed that Spy1622 could be involved in the response to acid stimuli.…”

Stress Physiology of Lactic Acid Bacteria

“…A GBS mutant of the CovSR ortholog, also known as CsrS/CsrR, displayed impaired viability in human serum and attenuated virulence in murine infection models (506,507). It has been hypothesized that the translocation of GBS from the acidic milieu of the vagina to neonatal tissues with a neutral pH signals the conversion from a colonizing to an invasive phenotype in a CsrRS-dependent manner (508). The CiaHR TCS of S. pneumoniae regulates many genes involved in competence development and virulence, including htrA (see above) (486).…”