Impact of plfB delation on the transcriptome of Streptococcus pneumoniae D39

Galactose is an important sugar for in vivo survival and virulence of important human pathogen Streptococcus pneumoniae, and pyruvate formate lyase (PFL) activity is crucial for galactose metabolism. Thus, the regulation of genes important for active PFL synthesis, pflA and pflB, was investigated. We identified six transcriptional regulators differentially expressed in ΔpflB and hypothesised that they are important for pflA or pflB regulation. Among these, CcpA, MerR2 and GntR family transcriptional regulators were directly involved in the regulation of pflA, pflB or both. It was found that CcpA is the transcriptional activator of pflB, and is the repressor of pflA on galactose. CcpA’s interaction with pflB did not require HPr-[Ser-P] but is enhanced by sodium formate, produced by the activity of PFL. The MerR2 is a repressor of both pflA and pflB, and sodium formate decreases MerR2 affinity for pflB promoter. In addition, MerR2 mediates ccpA expression mainly on glucose and to lesser degree on galactose, and MerR2 and CcpA interact for regulation of pflB. It was shown that both CcpA and MerR2 are required for pneumococcal colonisation and virulence. We also found that GntR represses pflB expression but its expression is not induced by any of the tested sugars, suggesting sugar independent regulation of pflB. Transcriptome comparison of the Streptococcus pneumoniae D39 ΔplfB to D39 wild type grown in CDM with 55mM Galactose One condition design comparision of two strains including a dye swap