The growth phase-dependent regulation of the pilus locus genes by two-component system TCS08 in Streptococcus pneumoniae

The two-component system TCS08 of Streptococcus pneumoniae contributes to the virulence in vivo and regulates phosphotransferase system (PTS) genes in an avirulent strain. However, its role in pathogenic strains and virulence mechanism are largely unknown. In this study, we constructed TCS08 knockout mutants in a serotype 4 encapsulated pathogenic strain TIGR4, and investigated target genes regulated by TCS08 through transcriptional profile analysis. Compared to TIGR4, expression of the rlrA islet genes (SP0461–SP0468) encoding pneumococcal pili was found to be up-regulated in the rr08 mutant (Δrr08). Further quantitative real-time PCR (qRT-PCR) analysis revealed that such induction was more significant when the strains were grown to late-logarithmic phase. In phenotype analyses, disruption of both hk08 and rr08 genes (ΔTCS08) resulted in increased adherence to human lung epithelial cells (A549) at 3 h at late-logarithmic and stationary phases. However, the invasion level of ΔTCS08 was reduced at different growth phases. Similar phenotype changes, though less significant, were also observed when the assays were performed on human nasopharyngeal epithelial cells (Detroit 562). These data suggest that TCS08 is involved in adhesion and invasion of host epithelial cells, which is likely mediated via regulation of the pilus locus genes in a growth phase-dependent manner.