Acidification of Cytoplasm in Escherichia coli Provides a Strategy to Cope with Stress and Facilitates Development of Antibiotic Resistance
Esmeralda Z. Reyes-Fernández, Shimon Schuldiner
Abstract
Abstract Awareness of the problem of antimicrobial resistance (AMR) has escalated, and drug-resistant infections are named among the most urgent issues facing clinicians today. Bacteria can acquire resistance to antibiotics by a variety of mechanisms that, at times, involve changes in their metabolic status, thus altering diverse biochemical reactions, many of them pH-dependent. In this work, we found that modulation of the cytoplasmic pH (pH i ) of Escherichia coli provides a thus far unexplored strategy to support resistance. We show here that the acidification of the cytoplasmic pH is a previously unrecognized consequence of the activation of the marRAB operon. The acidification itself contributes to the full implementation of the resistance phenotype. We measured the pH i of two resistant strains, developed in our laboratory, that carry mutations in marR that activate the marRAB operon. The pH i of both strains is lower than that of the wild type strain. Inactivation of the marRAB response in both strains weakens resistance, and pH i increases back to wild type levels. Likewise, we showed that exposure of wild type cells to weak acids that caused acidification of the cytoplasm induced a resistant phenotype, independent of the marRAB response. We speculate that the decrease of the cytoplasmic pH brought about by activation of the marRAB response provides a signaling mechanism that modifies metabolic pathways and serves to cope with stress and to lower metabolic costs.