Loss of Bacterial Cell Pole Stabilization in Caulobacter crescentus Sensitizes to Outer Membrane Stress and Peptidoglycan-Directed Antibiotics

Rod-shaped bacteria frequently localize proteins to one or both cellpoles in order to regulate processes such as chromosome replication or polar organ-elle development. However, the roles of polar factors in responses to extracellularstimuli have been generally unexplored. We employed chemical-genetic screening toprobe the interaction between one such factor fromCaulobacter crescentus, TipN,and extracellular stress and found that TipN is required for normal resistance of cellenvelope-directed antibiotics, including vancomycin which does not normally inhibitgrowth of Gram-negative bacteria. Forward genetic screening for suppressors of van-comycin sensitivity in the absence of TipN revealed the TonB-dependent receptorChvT as the mediator of vancomycin sensitivity. Loss of ChvT improved resistance tovancomycin and cefixime in the otherwise sensitive ΔtipNstrain. The activity of thetwo-component system regulating ChvT (ChvIG) was increased in ΔtipNcells relativeto the wild type under some, but not all, cell wall stress conditions that this strainwas sensitized to, in particular cefixime and detergent exposure. Together, these re-sults indicate that TipN contributes to cell envelope stress resistance in addition toits roles in intracellular development, and its loss influences signaling through theChvIG two-component system which has been co-opted as a sensor of cell wallstress inCaulobacter.