Date of Award
Doctor of Philosophy (PhD)
The Gram-positive bacterium Streptococcus pyogenes is a remarkably successful pathogen, capable of infecting numerous tissue sites within its human host. The ability of S. pyogenes to invade these different niches is, in part, due to the species’ ability to monitor various physical and chemical signals in its environment and alter its transcriptional profile in response to these differential conditions. As a member of the lactic acid bacteria, S. pyogenes has a simple fermentative metabolism and relies exclusively on a combination of homo-lactic and mixed acid fermentation as a means of generating energy in the cell. As a consequence of its fermentative metabolism, S. pyogenes produces several organic acid end products that, over time, accumulate in the surrounding environment, causing a substantial reduction in pH. Thus, growth of the bacterium itself results in a significant remodeling of its local tissue environment. It also indicates that over the course of infection, it must both adapt to its self-inflicted acid stress as well as exploit alternative carbon sources for survival. Although pH has been identified as a signal utilized by S. pyogenes to induce global transcriptional changes, the specific regulatory mechanisms behind this transcriptional remodeling have largely remained unclear. To further characterize the process of S. pyogenes’ pH adaptive response we have identified several novel pH-sensitive transcriptional regulators and analyzed their contribution to gene expression and S. pyogenes pathogenesis.
The malic enzyme pathway, which allows the cell to utilize malate as a carbon source for growth, consists of four genes in two adjacent operons, with the regulatory TCS MaeKR being required for the expression of the genes encoding a malate permease (maeP) and malic enzyme (maeE). Results show that expression of the maePE operon is influenced independently by external malate concentrations and pH in a MaeK-dependent mechanism. The ME genes are additionally regulated by a unique CcpA-independent form of catabolite repression which involves the PTS proteins PtsI and HPr. Furthermore, in vivo experiments demonstrate that loss of any individual ME gene has a significant effect on the outcome of a soft tissue infection.
The secreted toxins SPN and SLO have been shown to contribute to S. pyogenes cytotoxicity and virulence in multiple models of pathogenesis, however little information is known about the specific regulatory mechanism that control expression of these toxins. Our work has determined that the growth-phase pattern of expression of the spn/slo operon is regulated by environmental pH. Additionally, this regulation requires both the CovRS two-component system as well as an additional protein, RocA. Additional data suggests that RocA does not function as a traditional histidine kinase, despite high structural and sequence homology to known histidine kinases such as CovS. However, all three regulatory proteins are required for the pH-mediated regulation of this virulence operon.
Chair and Committee
Michael G Caparon
David Hunstad, Christina Stallings, Jeff Henderson, Joseph Vogel, Amanda Lewis
Paluscio, Elyse, "Adaptive Mechanisms of Niche Remodeling in Streptococcus pyogenes" (2015). Arts & Sciences Electronic Theses and Dissertations. 674.