Characterization of a Quorum Sensing System Important for Pneumococcal Pathogenesis

Quorum Sensing (QS), or bacterial communication by intercellular chemical signaling, is a process common to many (if not most) bacterial species; yet, it is unclear how QS signaling pathways contribute to virulence in many clinically significant pathogens. The Federle lab has helped to characterize a family of transcriptional regulators, known as Rgg proteins, as mediators of QS. We and others have shown the importance of Rgg proteins in multiple species of streptococci in regulating expression of genes that may enhance their ability to colonize and infect the host. The role of the Rgg proteins in the pathogenic lifestyle of Streptococcus pneumoniae is just beginning to be investigated. Published genome-level mutagenesis studies indicate Rgg proteins in this organism are critical in models of infection. Additionally, recent studies have confirmed the contribution of Rgg0141 to bacterial fitness in vivo. However, it is unclear which genetic factors regulated by Rgg0141 are responsible for this virulence phenotype. Using RNA-sequencing technology, we have identified numerous virulence factors belonging to the Rgg0141 regulon, such as the manganese transport system psaBCA, the pore-forming toxin, pneumolysin (ply), and the previously described bacteriocin containing operon vp1BCD. Luciferase reporter assays have allowed us to monitor QS system induction and regulation of target genes under a variety of conditions, specifically in the presence and absence of the signaling pheromone SHP0141 and under varying manganese concentrations. Using an infection model of pneumonia, we have demonstrated the importance of Rgg0141 and vp1BC for competitive fitness in the lungs and blood of mice. Additionally, we have taken a biochemical approach in order to describe the binding kinetics of Rgg0141-SHP0141 to DNA. The methodology of our studies can be extended to other bacteria, as QS occurs in many other bacterial populations and the Rgg proteins can be found in a variety of bacterial species. Understanding the molecular networks under QS regulation is the first step towards developing novel therapeutic approaches that could slow down the development of drug resistance and be more effective at combating clinically significant pathogens.