Methionine-mediated gene expression and characterization of the CmhR regulon in Streptococcus pneumoniae

In this study, we investigated the transcriptomic response of Streptococcus pneumoniae D39 to methionine. Transcriptome comparison of the S. pneumoniae D39 wild-type grown in chemically defined medium (CDM) with 0mM to 10mM methionine revealed the elevated expression of various genes/operons involved in methionine synthesis and transport (fhs, folD, gshT, metA, metB, metEF, metQ, tcyB, spd-0150, spd-0431, and spd-0618). We further demonstrated by β-galactosidase assays and quantitative RT-PCR studies that the transcriptional regulator, CmhR (SPD-0588) acts as a transcriptional activator of the fhs, folD, metB, metEF, metQ, and spd-0431 genes. We identified a putative regulatory site of CmhR in the promoter region of CmhR regulated genes and this CmhR site was further confirmed by promoter mutational experiments. Comparison of the Streptococcus pneumoniae D39 wild-type grown in CDM with 10mM added methionine to D39 wild-type grown in CDM with 0mM added methionine. Two conditions design comparison of one strain including a dye swap.