ABC Transporters Required for Export of Wall Teichoic Acids Do Not Discriminate between Different Main Chain Polymers

The cell envelopes of Gram-positive bacteria comprise two major constituents, peptidoglycan and teichoic acids. Wall teichoic acids (WTAs) are anionic glycophosphate polymers that play important roles in bacterial cell growth, division, and pathogenesis. They are synthesized intracellularly and exported by an ABC transporter to the cell surface, where they are covalently attached to peptidoglycan. We address here the substrate specificity of WTA transporters by substituting the Bacillus subtilis homologue, TagGH(Bs), with the Staphylococcus aureus homologue, TarGH(Sa). These transporters export structurally different substrates in their indigenous organisms, but we show that TarGH(Sa) can substitute for the B. subtilis transporter. Hence, substrate specificity does not depend on the WTA main chain polymer structure but may be determined by the conserved diphospholipid-linked disaccharide portion of the WTA precursor. We also show that the complemented B. subtilis strain becomes susceptible to a S. aureus-specific antibiotic, demonstrating that the S. aureus WTA transporter is the sole target of this compound.