Ni(2+)-Dependent and PsaR-Mediated Regulation of the Virulence Genes pcpA, psaBCA, and prtA in Streptococcus pneumoniae

Previous studies have shown that the transcriptional regulator PsaR regulates the expression of the PsaR regulon consisting of genes encoding choline binding protein (PcpA), the extracellular serine protease (PrtA), and the Mn(2+)-uptake system (PsaBCA), in the presence of manganese (Mn(2+)), zinc (Zn(2+)), and cobalt (Co(2+)). In this study, we explore the Ni(2+)-dependent regulation of the PsaR regulon. We have demonstrated by qRT-PCR analysis, metal accumulation assays, β-galactosidase assays, and electrophoretic mobility shift assays that an elevated concentration of Ni(2+) leads to strong induction of the PsaR regulon. Our ICP-MS data show that the Ni(2+)-dependent expression of the PsaR regulon is directly linked to high, cell-associated, concentration of Ni(2+), which reduces the cell-associated concentration of Mn(2+). In vitro studies with the purified PsaR protein showed that Ni(2+) diminishes the Mn(2+)-dependent interaction of PsaR to the promoter regions of its target genes, confirming an opposite effect of Mn(2+) and Ni(2+) in the regulation of the PsaR regulon. Additionally, the Ni(2+)-dependent role of PsaR in the regulation of the PsaR regulon was studied by transcriptome analysis.