Today, the fight against antibiotic resistant bacteria is more important than ever as they continuously adapt to our countermeasures designed to eliminate bacterial infections. New antibacterial strategies are needed to fight back resistant clinical isolates. Here we intend to help in this fight by illuminating principles of antibiotic permeation using the Gram-negative (diderm) model organism Caulobacter crescentus, a non-pathogenic alpha-proteobacterium. As an oligotrophic and environmental bacterium, it elaborates many systems to import nutrients while expelling toxic molecules and waste products with high efficiency from the environment across the outer membrane (OM), via porins or the TonB-dependent receptors (TBDRs) and antibiotic efflux pumps, respectively. C. crescentus encodes >60 TBDRs , that are differentially expressed depending on the life stage or environment and harbor a broad variety of structures. Their precise role and their regulation remain cryptic and are still under investigation, raising the question of their need in such a number and diversity in this strain. In my project, we selected several TBDRs to study and replaced their endogenous promoters by a strong constitutive promoter to ensure expression. We performed an antibiotic sensibility assay to investigate the possible substrates of these TBDRs. During our investigations, we detected an OM structural overload of proteins that led to its destabilization and trigger feedback regulatory mechanisms. This led us to explore the bacterial response to forced TBDR expression by strong promoters, as well as massive upregulation of an efflux pump and other OM saturating systems. To probe the stress response of C. crescentus, we used a reporter of expression, a regulatory small RNA named chvR and thus its own regulatory network through a two- component regulatory system: involving the ChvI response regulator and the ChvG sensory kinase. Finally, because existing literature suggests that L-alanine and glucose could be natural TBDR substrate to be use as carbon source by the cells, we wanted to confirm the specificity to one TBDRs or infirm it as many TBDRs could substrates. To explore this idea,4 we decided to assess the fitness cost of the presence of the selected subset of strains expressing TBDRs in minimal media with either glucose or L-alanine. In summary, my project characterized the spectrum of antibiotic import by some TBDRs, the stress response to high OM protein load and finally natural TBDR substrate(s).