Ni2+-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 Mn2+-uptake system (PsaBCA), in the presence of manganese (Mn2+), zinc (Zn2+), and cobalt (Co2+). In this study, we explore the Ni2+-dependent regulation of the PsaR regulon. We have demonstrated by qRT-PCR analysis, metal accumulation assays, beta-galactosidase assays, and electrophoretic mobility shift assays that an elevated concentration of Ni2+ leads to strong induction of the PsaR regulon. Our ICP-MS data show that the Ni2+-dependent expression of the PsaR regulon is directly linked to high, cell-associated, concentration of Ni2+, which reduces the cell-associated concentration of Mn2+. In vitro studies with the purified PsaR protein showed that Ni2+ diminishes the Mn2+-dependent interaction of PsaR to the promoter regions of its target genes, confirming an opposite effect of Mn2+ and Ni2+ in the regulation of the PsaR regulon. Additionally, the Ni2+-dependent role of PsaR in the regulation of the PsaR regulon was studied by transcriptome analysis.