The Dynamic Streptococcus Pyogenes Transcriptome in the Host Cell Environment and Contributions by Phage

This thesis investigates the transcriptional responses of Streptococcus pyogenes in the pharyngeal environment and characterizes two transcriptional regulators involved in the adaptive response to the host. Furthermore, this thesis explores the potential role of integrated prophage on the streptococcal transcriptome. We are specifically interested in global regulatory systems in group A streptococci and how they impact virulence regulation. With this work, we hoped to identify new regulatory elements involved in the infection process. The first objective of this thesis was to determine the transcriptional shift induced in streptococci upon introduction into the in vitro host environment. Using three time points, we examined the dynamic transcriptome remodeling program that streptococci undergo following exposure to cell-free pharyngeal culture supernatants or during co-culture with intact pharyngeal monolayers. These studies highlighted that streptococci modulate expression of virulence factors in the host environment using a combination of stand-alone regulators (most of which are uncharacterized) and two-component regulatory systems. The next phase of this work involved characterizing two of the stand-alone regulators identified in our transcriptome screen. The first spy1215 encodes a sirtuin-like deacetylase that is homologous to a repressor of virulence in the malarial parasite Plasmodium falciparum. Our work presents the first evidence of a direct link between a bacterial sirtuin (Spy1215) and virulence regulation. Interestingly, Spy1215-mediated virulence repression was determined to be dependent on signals from pharyngeal cells in S. pyogenes. The second regulator spy1755 was found to be an activator of fatty acid biosynthesis in group A streptococci and required for normal growth rates in laboratory media. Finally, we endeavored to elucidate the role of integrated prophage in the regulation of streptococcal gene expression. Using the first S. pyogenes strain cured of all phage, we explored the effect of phage deletion on the streptococcal transcriptome during early and late exponential growth in laboratory media. We found a limited effect on gene expression in the absence of integrated phage. The genes whose expression was most affected by phage deletion were found to lie downstream of phage insertion sites. Overall, this work supports observations thus far that the streptococcal strain cured of all phage displays a limited phenotype via numerous measures in vitro and in vivo