Catabolism of aromatic β-glucosides by bacteria can lead to antibiotics resistance

Involvement of BglG in Lipopolysaccharides (LPS) Synthesis and Transport in Stationary Phase in E. coli

BglG, an RNA binding regulatory protein encoded by the β-glucoside (bgl) operon of E. coli is known to be involved in the regulation of several metabolic functions in stationary phase. A genome-wide comparative transcriptome analysis performed earlier between a ∆bglG strain and its isogenic WT counterpart revealed that genes involved in lipopolysaccharide (LPS) biosynthesis and transport were significantly down-regulated in the absence of BglG in stationary phase, suggesting a role for BglG in their regulation. We have investigated the involvement of BglG in LPS biosynthesis and transport. Consistent with the down-regulation of LPS synthesis and transport genes, the ∆bglG strain showed a loss of permeability barrier specifically in stationary phase, which could be rescued by introduction of wild type bglG on a plasmid. A search for a putative transcription factor involved in the regulation mediated by BglG led to the identification of GadE, which is one of the primary positive regulators of pH homeostasis and LPS core biosynthesis. Using RNA mobility shift and stability assays, we show that BglG binds specifically to gadE mRNA and enhances its stability. Consistent with this, loss of gadE leads to a partial defect in permeability. Based on our findings, we propose a model for the molecular mechanism involved in the regulation on LPS synthesis and transport by BglG.

An Intertwined Network of Regulation Controls Membrane Permeability Including Drug Influx and Efflux in Enterobacteriaceae

The transport of small molecules across membranes is a pivotal step for controlling the drug concentration into the bacterial cell and it efficiently contributes to the antibiotic susceptibility in Enterobacteriaceae. Two types of membrane transports, passive and active, usually represented by porins and efflux pumps, are involved in this process. Importantly, the expression of these transporters and channels are modulated by an armamentarium of tangled regulatory systems. Among them, Helix-turn-Helix (HTH) family regulators (including the AraC/XylS family) and the two-component systems (TCS) play a key role in bacterial adaptation to environmental stresses and can manage a decrease of porin expression associated with an increase of efflux transporters expression. In the present review, we highlight some recent genetic and functional studies that have substantially contributed to our better understanding of the sophisticated mechanisms controlling the transport of small solutes (antibiotics) across the membrane of Enterobacteriaceae. This information is discussed, taking into account the worrying context of clinical antibiotic resistance and fitness of bacterial pathogens. The localization and relevance of mutations identified in the respective regulation cascades in clinical resistant strains are discussed. The possible way to bypass the membrane/transport barriers is described in the perspective of developing new therapeutic targets to combat bacterial resistance.