Investigating the role of Rgg Transcriptional Regulators in Streptococcus pneumoniae

Rgg is a group of transcriptional regulators found in Gram positive bacteria, and they play diverse roles including in metabolism and virulence in a range of bacteria. However, their roles in the important human pathogen Streptococcus pneumoniae are not known in detail. To assess the functional importance of Rgg homologs in S. pneumoniae, targeted mutation was used for the deletion of two rgg genes, SPD_0999 and SPD_1518 (rgg0999 and rgg1518). In vitro analysis showed that under microaerobic conditions, the mutants were attenuated on mannose and galactose compared to the wild type, whereas their growth profiles were similar to that of wild type in BHI (Brain Heart Infusion) and CDM (Chemically Defined Medium) containing glucose. In vivo analysis of Rgg mutants showed that both SPD_0999 and SPD_1518 are required for pneumococcal virulence. All mice infected intranasaly with either Rgg mutant survived significantly longer and had less bacteria in their blood compared to the wild type. Moreover, microarray analysis using cultures grown on galactose and mannose showed that the largest number of differentially expressed genes in rgg mutant strains was seen on galactose, especially those encoding for essential physiological functions and virulence related genes such as the capsular locus. Electrophoretic mobility shift assay, and transcriptional lacZ-fusions are the most appropriate techniques used for investigating the regulating role of genes in transcriptional regulation. In this study, the results show that Rgg1518 has a direct ability to control the transcription of capsule locus genes (SPD_0315-SPD_0328) and the data also show that the protein Rgg1518 acts as an activator for capsule locus genes in presence of galactose. Therefore, so far the available results show that Rggs encoded by SPD_0999 or SPD_1518 play a major role in pneumococcal virulence.