Streptococcus pneumoniae PstS production is phosphate responsive and enhanced during growth in the murine peritoneal cavity

Differential display-PCR (DDPCR) was used to identify a Streptococcus pneum oniae gene with enhanced transcription during growth in the murine peritone al cavity. Northern dot blot analysis and comparative densitometry confirme d a 1.8-fold increase in expression of the encoded sequence following murin e peritoneal culture (MPC) versus laboratory culture or control culture (CC ). Sequencing and basic local alignment search tool analysis identified the DDPCR fragment as pstS, the phosphate-binding protein of a high-affinity p hosphate uptake system. PCR amplification of the complete pstS gene followe d by restriction analysis and sequencing suggests a high level of conservat ion between strains and serotypes. Quantitative immunodot blotting using an tiserum to recombinant PstS (rPstS) demonstrated an approximately twofold i ncrease in PAS production during MPC from that during CCs, a finding consis tent with the low levels of phosphate observed in the peritoneum. Moreover, immunodot blot and Northern analysis demonstrated phosphate-dependent prod uction of PstS in six of seven strains examined. These results identify pst S expression as responsive to the MPC environment and extracellular phospha te concentrations. Presently, it remains unclear if phosphate concentration s in vivo contribute to the regulation of pstS. Finally, polyclonal antiser um to rPstS did not inhibit growth of the pneumococcus in vitro, suggesting that antibodies do not block phosphate uptake; moreover, vaccination of mi ce with rPstS did not protect against intraperitoneal challenge as assessed by the 50% lethal dose.