title: Active efflux of bile salts by Escherichia coli.
abstract: Enteric bacteria such as Escherichia coli must tolerate high levels of bile salts, powerful detergents that disrupt biological membranes. The outer membrane barrier of gram-negative bacteria plays an important role in this resistance, but ultimately it can only retard the influx of bile salts. We therefore examined whether E. coli possessed an energy-dependent efflux mechanism for these compounds. Intact cells of E. coli K-12 appeared to pump out chenodeoxycholate, since its intracellular accumulation increased more than twofold upon deenergization of the cytoplasmic membrane by a proton conductor. Growth inhibition by bile salts and accumulation levels of chenodeoxycholate increased when mutations inactivating the acrAB and emrAB gene clusters were introduced. The AcrAB system especially appeared to play a significant role in bile acid efflux. However, another efflux system(s) also plays an important role, since the accumulation level of chenodeoxycholate increased strongly upon deenergization of acrA emrB double mutant cells. Everted membrane vesicles accumulated taurocholate in an energy-dependent manner, apparently consuming delta pH without affecting delta psi. The efflux thus appears to be catalyzed by a proton antiporter. Accumulation by the everted membrane vesicles was not decreased by mutations in acr and emrB genes and presumably reflects activity of the unknown system seen in intact cells. It followed saturation kinetics with Vmax and Km values in the neighborhood of 0.3 nmol min(-1) mg of protein(-1) and 50 microM, respectively.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720-3206, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Thanassi
authors.forename: L W
authors.initials: LW
authors.lastname: Cheng
authors.forename: H
authors.initials: H
authors.lastname: Nikaido
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001647:Bile Acids and Salts / Q000378:metabolism*; D001692:Biological Transport; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002352:Carrier Proteins; D003840:Deoxycholic Acid / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D008074:Lipoproteins / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D018272:Porins / Q000235:genetics; D011189:Potassium Chloride / Q000494:pharmacology; D018892:Proton-Motive Force; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D001647:Bile Acids and Salts; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002352:Carrier Proteins; D003840:Deoxycholic Acid; D029968:Escherichia coli Proteins; D008051:Lipid Bilayers; D008074:Lipoproteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D018272:Porins; D011189:Potassium Chloride; D014475:Uncoupling Agents; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C489681:EmrA protein, E coli; C077168:emrA protein, Bacteria; C077169:VceB protein, Vibrio cholerae