The Inactivation of Sensitizes to Perturbations in Lipopolysaccharide Transport

The outer membrane channel TolC complexes with several inner membrane efflux pumps to export compounds across the cell envelope. All components of these complexes are essential for robust efflux activity, yet is more sensitive to antimicrobial compounds when is inactivated compared to the inactivation of genes encoding the inner membrane drug efflux pumps. While investigating these susceptibility differences, we identified a distinct class of inhibitors targeting the core-lipopolysaccharide translocase, MsbA. We show that null mutants are sensitized to structurally unrelated MsbA inhibitors and knockdown, highlighting a synthetic-sick interaction. Phenotypic profiling revealed that inactivation induced cell envelope softening and increased outer membrane permeability. Overall, this work identified a chemical probe of MsbA, revealed that is associated with cell envelope mechanics and integrity, and highlighted that these findings should be considered when using null mutants to study efflux deficiency.