Chemical inhibition of cell surface modification sensitizes bacteria to phage infection†

Many bacteriophages that infect Gram-positive bacteria rely on the bacterial cell surface polymer wall teichoic acid (WTA) as a receptor. However, some bacteria modulate their cell wall with D-alanine residues, which can disrupt phage adsorption. The prevalence and significance of WTA alanylation as an anti-phage defense is unknown. A chemical inhibitor of WTA D-alanylation could be employed to efficiently screen phage-host combinations for those that exhibit alanylation-dependent infections. Since the incorporation of D-alanine residues into the cell wall requires the activity of D-alanine:alanyl carrier protein ligase (DltA), a DltA inhibitor was employed as this tool. Herein, we found that a chemical probe inhibiting DltA activity impeded bacterial cell wall alanylation and enhanced infectivity of many phages against Bacillus subtilis, including phages Phi29, SPP1, SPO1, SP50, and Goe2. This finding reveals the breadth of immunity conferred by WTA alanylation in B. subtilis, which was previously known to impact only phages Phi29 and SPP1, but not SPO1, SP50, or Goe2. DltA inhibition selectively promoted infection by several phages that bind WTA, having no impact on the flagellotropic phage PBS1. Unexpectedly, DltA inhibition also had no effect on phage SP10, which binds to WTA. This selective chemical tool has the potential to unravel bacteriophage interactions with bacteria, leading to improved phage therapies in the future.