Investigating Synthetic Lethal Interactions with the Wall Teichoic Acid Pathway of Staphylococcus aureus

The peptidoglycan of many Gram-positive bacteria is densely functionalized with anionic glycopolymers called wall teichoic acids (WTAs). Recent studies have shown that these polymers play crucial roles in cell shape determination, regulation of cell division, and other fundamental aspects of Gram-positive bacterial physiology. Furthermore, in pathogens they are important in host infection and play key roles in antibiotic resistance. In many cases, precise mechanisms for WTA involvement in these processes have not been established. In order to better understand the roles of WTAs in the biology of the human pathogen Staphylococcus aureus, we sought to identify their interactions with other cellular pathways. By employing a transposon screen, we found that lipoteichoic acid (LTA) synthesis, D-alanylation of teichoic acids, cell wall stress sensors, CAAX-like proteases, and peptidoglycan biosynthesis were all synthetically lethal with depletion of WTAs in Staphylococcus aureus . Further investigations revealed that several genes required when WTAs were depleted were not essential when LTAs were removed. Unexpectedly, TA D-alanylation, became essential in the absence of WTAs, but not LTAs. Examination of terminal phenotypes following WTA depletion revealed that strains lacking LTA D-alanine esters died from envelope rupture during ongoing cell division whereas strains lacking LTAs were unable to form Z rings, stopped dividing, and had altered PG biosynthesis. Finally, we designed and implemented parallel, pathway-specific chemical screens to identify inhibitors that specifically kill mutants deficient in WTAs or D-alanylation of TAs. In addition to elucidating new interactions between cell envelope pathways, and establishing distinct roles LTAs and WTAs in the cell envelope of S. aureus, these experiments provide a list of potential targets and a strategy for identifying inhibitors for these targets, in compound combinations as therapeutics against antibiotic-resistant S. aureus infections.