Strain-specific impact of PsaR of Streptococcus pneumoniae on global gene expression and virulence

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. In addition, we found 31 genes to be regulated by PsaR in D39 only, most strikingly a cellobiose-specific phosphotrainsferase system (PTS) and a putative bacterocin operon (sp0142-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 Delta psaR: D39 Delta psaR had an initial advantage in survival in the lungs. Conversely, TIGR4 Delta psaR-infected mice had significantly lower bacterial loads at 24 h only. Finally, during experimental bacteraemia, D39 Delta psaR-infected mice had significantly lower bacterial loads in the bloodstream than wt-infected mice for the first 24 h of infection. TIGR4 Delta psaR showed attenuation at 36 h 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 bacteraemia in mice.