Enhanced tolerance of metal-sequestering agents by reconfiguration of the Staphylococcus aureus cell wall

Chelators possess antibacterial properties linked to metal-sequestration, simulating the action of nutritional immunity in preventing infection. To gain further insight into bacterial adaptation to metal restriction, we isolated mutants of Staphylococcus aureus with enhanced resistance to two synthetic chelators with therapeutic potential. Mutations were identified that altered peptidoglycan metabolism and teichoic acid modification, crucially affecting the activity of PBP2 and eliminating FmtA or VraF functionality. The resulting strains showed increased cell wall thickness, modified cell surface charge and varied in their susceptibility to cell wall-targeting agents. In those mutants lacking either FmtA or VraF, the modifications substantially increased cell surface-associated calcium, offering protection against the loss of manganese preferentially targeted by both chelators. Our phenotypic and cellular metal analyses identify the cell envelope of S. aureus as a key target for metal-sequestering molecules. Peptidoglycan and teichoic acids, in particular, serve as key repositories for a subset of metal ions that safeguard against deprivation and can be altered to augment resistance to antibacterial chelators.