Co-chaperone-mediated post-translational control of efflux pump induction underlies adaptive ß-lactam resistance in Caulobacter crescentus [ChIP-seq]
The acquisition of multi-drug resistance (MDR) determinants jeopardizes treatment of bacterial infections with antibiotics. The tripartite efflux pump AcrAB-NodT confers adaptive MDR in the non-pathogenic a-proteobacterium Caulobacter crescentus via transcriptional induction by first-generation quinolone antibiotics. We discovered that overexpression of AcrAB-NodT by mutation or exogenous inducers confers resistance to cephalosporin and penicillin (ß-lactam) antibiotics. Combining two-step mutagenesis-sequencing (Mut-Seq) and cephalosporin-resistant point mutants, we dissected how TipR targets a common operator of divergent tipR and acrAB-nodT promoter in adaptive and/or potentiated AcrAB-NodT-directed efflux. Chemical screening identified compounds that either interfere with DNA-binding by TipR  or induce its ClpXP-dependent proteolytic turnover. We found that long-term induction of AcrAB-NodT disfigures the envelope and that homeostatic control by TipR includes co-induction of the DnaJ-like co-chaperone DjlA, to boost pump assembly and/or capacity in anticipation of envelope stress. Thus, the adaptive MDR regulatory circuitry reconciles drug efflux with co-chaperone function for trans-envelope assemblies and maintenance. Overall design: Examination of TipR and DjlA-HA whole genome binding/occupancy (ChIP-Seq) in the model organism Caulobacter crescentus.