N-acetylgalatosamine-Mediated Regulation of the aga Operon by AgaR in Streptococcus pneumoniae

Abstract

Here, we analyze the transcriptomic response of <i>Streptococcus pneumoniae</i> D39 to N-acetylgalactosamine (NAGa). Transcriptome comparison of <i>S. pneumoniae</i> D39 grown in NAGaM17 (0.5% NAGa + M17) to that grown in GM17 (0.5% Glucose + M17) revealed the elevated expression of various carbon metabolic genes/operons, including a PTS operon (denoted here as the <i>aga</i> operon), which is putatively involved in NAGa transport and utilization, in the presence of NAGa. We further studied the role of a GntR-family transcriptional regulator (denoted here as AgaR) in the regulation of <i>aga</i> operon. Our transcriptome and RT-PCR data suggest the role of AgaR as a transcriptional repressor of the <i>aga</i> operon. We predicted a 20-bp operator site of AagR (5'-ATAATTAATATAACAACAAA-3') in the promoter region of the <i>aga</i> operon (P<i>bgaC</i>), which was further verified by mutating the AgaR operator site in the respective promoter. The role of CcpA in the additional regulation of the <i>aga</i> operon was elucidated by further transcriptome analyses and confirmed by quantitative RT-PCR.