Mn2+-Dependent Regulation of Multiple Genes in Streptococcus pneumoniae through PsaR and the Resultant Impact on Virulence

The concentration of Mn 2+ is 1,000-fold higher in secretions than it is at internal sites of the body, making it a potential signal by which bacteria can sense a shift from a mucosal environment to a more invasive site. PsaR, a metal-dependent regulator in Streptococcus pneumoniae , was found to negatively affect the transcription of psaBCA , pcpA , rrgA , rrgB , rrgC , srtBCD , and rlrA in the presence of Mn 2+ . psaBCA encode an ABC-type transporter for Mn 2+ .  pcpA , rrgA , rrgB , and rrgC encode several outer surface proteins. srtBCD encode a cluster of sortase enzymes, and rlrA encodes a transcriptional regulator. Steady-state RNA levels are high under low Mn 2+ concentrations in the wild-type strain and are elevated under both high and low Mn 2+ concentrations in a psaR mutant strain. RlrA is an activator of rrgA , rrgB , rrgC , and srtBCD (D. Hava and A. Camilli, Mol. Microbiol. 45: 1389-1406, 2002), suggesting that PsaR may indirectly control these genes through rlrA , while PsaR-dependent repression of psaBCA , pcpA , and rlrA transcription is direct. The impact of Mn 2+ -dependent regulation on virulence was further examined in mouse models of pneumonia and nasopharyngeal carriage. The abilities of Δ psaR , pcpA , and Δ psaR Δ pcpA mutant strains to colonize the lung were reduced compared to those of the wild type, confirming that both PcpA-mediated gene regulation and PsaR-mediated gene regulation are required for full virulence in the establishment of pneumonia. Neither PcpA nor PsaR was found to be required for colonization of the nasopharynx in a carriage model. This is the first demonstration of Mn 2+ acting as a signal for the expression of virulence factors within different host sites.