title: Reduction of cellular stress by TolC-dependent efflux pumps in Escherichia coli indicated by BaeSR and CpxARP activation of spy in efflux mutants.
abstract: Escherichia coli has nine inner membrane efflux pumps which complex with the outer membrane protein TolC and cognate membrane fusion proteins to form tripartite transperiplasmic pumps with diverse functions, including the expulsion of antibiotics. We recently observed that tolC mutants have elevated activities for three stress response regulators, MarA, SoxS, and Rob, and we suggested that TolC-dependent efflux is required to prevent the accumulation of stressful cellular metabolites. Here, we used spy::lacZ fusions to show that two systems for sensing/repairing extracytoplasmic stress, BaeRS and CpxARP, are activated in the absence of TolC-dependent efflux. In either tolC mutants or bacteria with mutations in the genes for four TolC-dependent efflux pumps, spy expression was increased 6- to 8-fold. spy encodes a periplasmic chaperone regulated by the BaeRS and CpxARP stress response systems. The overexpression of spy in tolC or multiple efflux pump mutants also depended on these systems. spy overexpression was not due to acetate, ethanol, or indole accumulation, since external acetate had only a minor effect on wild-type cells, ethanol had a large effect that was not CpxA dependent, and a tolC tnaA mutant which cannot accumulate internal indole overexpressed spy. We propose that, unless TolC-dependent pumps excrete certain metabolites, the metabolites accumulate and activate at least five different stress response systems.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA. jlrosner@helix.nih.gov
authors.forename: Judah L
authors.initials: JL
authors.lastname: Rosner
authors.forename: Robert G
authors.initials: RG
authors.lastname: Martin
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D024901:Drug Resistance, Multiple, Bacterial; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D033903:Periplasmic Proteins / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C560503:BaeR protein, E coli; C491730:CpxP protein, E coli; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033903:Periplasmic Proteins; C104888:Spy protein, E coli; D015534:Trans-Activators; C073126:tolC protein, E coli; C085504:CpxR protein, Bacteria; D011494:Protein Kinases; C490475:CpxA protein, E coli