Mechanistic investigation of novel virulence related proteins produced by the pathogens <i>Streptococcus pneumoniae</i> and <i>Staphylococcus aureus</i>.

Characterising the genetic networks that regulate bacterial virulence can help widening our understanding of pathogenicity and highlight potential targets for the development of new therapeutics. Genome-wide association studies and functional genomics have been deployed to identify the genetic determinants of virulence, and specifically toxicity, in the clinically relevant pathogens Streptococcus pneumoniae (S. pneumoniae) and Staphylococcus aureus (S. aureus). However, these information can be applied to further our understanding of pathogenicity only if we unravel the mechanisms whereby the identified variants affect toxicity. This study aimed at filling the gap between functional genomics and mechanistic insights by understanding how the recently identified proteins ZomB and MspA affect virulence respectively in S. pneumoniae and S. aureus. ZomB is a UvrD-like helicase which was found to be significantly associated with the production of the toxin pneumolysin in S. pneumoniae. This study has confirmed ZomB to be a positive regulator of pneumolysin transcription. ZomB has been shown to interact with CiaR, a regulator of competence, virulence and cell wall synthesis, although such interaction does not explain the mechanism of ZomB’s transcriptional regulation. Other protein partners have also been identified which with further work could elucidate ZomB’s effect on pneumolysin expression. A S. aureus small membrane protein, MspA, had been shown to affect not only toxin production but also membrane stability and iron homeostasis. This work has developed different approaches to characterise the expression and localisation of the MspA protein and to identify its protein partners. The data here presented demonstrates that MspA regulates the abundance of the key cell wall component lipoteichoic acid (LTA) by interacting with the LTA synthetic enzymes and interfering with the formation of their enzymatic complex. This role of the MspA protein is also thought to underlie the protein’s effect on virulence. This study furthers our understanding of the different mechanisms whereby bacterial proteins can affect the production of toxins and virulence factors