Investigating genetic interaction networks of Staphylococcus aureus cell envelope proteins

Abstract

The prevalence of antibiotic resistant Staphylococcus aureus, particularly methicillin-resistant Staphylococcus aureus (MRSA), is a growing public threat and has made the pursuit of novel antibacterial therapeutics a necessity. The bacterial cell envelope is a complex structure comprised of the peptidoglycan cell wall, membrane-bound enzymes, and teichoic acids. The teichoic acids, particularly the lipoteichoic acids (LTAs), remain an underexplored target space for antibiotic discovery. This thesis describes a genetic approach to identify potential targets for antibiotic discovery and address antibiotic resistance by investigating the genetic interaction networks of four genes involved in the biosynthesis and regulation of the S. aureus cell envelope. In this work, I characterized the growth and morphology of a mutant depleted of the LTA synthase, ltaS, in two suppressor backgrounds. I found that cells depleted of LtaS that have poor viability and multiple cell division and morphological defects. However, the viability and morphological defects of this cell improve when in a ∆cozEb or ∆sgtB suppressor background. I found that the growth, cell division defects, and morphologies of the ∆ltaS ∆cozEb and ∆ltaS ∆sgtB strains are very different from each other, with the ∆ltaS ∆cozEb having a more similar growth and morphology to wild type cells. I also identified, using a TnSeq approach, an enriched gene encoding a proposed adaptor for the Sle1 cell wall hydrolase, cxaR, in the ∆ltaS ∆cozEb dataset. Furthermore, I identified the mecA and tarO loci, using the TnSeq approach, as depleted in the ∆cozEb and ∆cozEa datasets, respectively. I then collaborated with a post-doc in our lab to validate these depleted loci from these two datasets and show that cozEb and cozEa are unlikely to have completely redundant cellular functions in S. aureus. Together, this work advances our understanding of the biology for the S. aureus cell envelope. Furthermore, this work highlights a novel strategy to identify potential targets for future antibiotic therapies by exploiting the genetic interaction network of cell envelope proteins.