Synergistic action of peptidoglycan and teichoic acid synthesis inhibitors leads to cell death by oxidative damage

Peptidoglycan (PG) is the primary structural component of the bacterial cell wall. However, many bacteria can switch into a wall-deficient "L-form" state, whereby they grow without PG synthesis and become completely resistant to cell-wall-targeting antibiotics. Teichoic acids (TAs) are major glycopolymers of Gram-positive bacteria that are attached to either the PG wall (WTA) or the lipid membrane (LTA). We show that L-form growth does not require either WTA or LTA. However, it does require the TagO protein, which initiates the synthesis of WTA. Inhibiting TagO with the antibiotic tunicamycin triggers a metabolic shift resulting in oxidative damage-mediated cell death, and this is highly synergistic with perturbations of the PG synthetic system. UDP-GlcNAc, a key precursor for both PG and TA synthesis, controls a metabolic switch leading either to balanced growth or oxidative damage. Our results demonstrate the pivotal role of UDP-GlcNAc in the mechanism of killing by cell wall inhibition.