title: TolC is involved in enterobactin efflux across the outer membrane of Escherichia coli.
abstract: Escherichia coli excretes the catecholate siderophore enterobactin in response to iron deprivation. While the mechanisms underlying enterobactin biosynthesis and ferric enterobactin uptake and utilization are widely understood, nearly nothing is known about how enterobactin is exported from the cell. Mutant and high-performance liquid chromatography analyses demonstrated that the outer membrane channel tunnel protein TolC but none of the respective seven resistance nodulation cell division (RND) proteins CusA, AcrB, AcrD, AcrF, MdtF (YhiV), or the twin RND MdtBC (YegNO) was essential for enterobactin export across the outer membrane. Mutant E. coli strains with additional deletion of tolC or the major facilitator entS were growth deficient in iron-depleted medium. Strains with deletion of tolC or entS, but not with deletion of genes encoding RND transporters, excreted very little enterobactin into the growth medium. Enterobactin excretion in E. coli is thus probably a two-step process involving the major facilitator EntS and the outer membrane channel tunnel protein TolC. Quantitative reverse transcription-PCR analysis of gene-specific transcripts showed no significant changes in tolC expression upon iron depletion. However, iron starvation led to increased expression of the RND gene mdtF and a decrease in acrD.
authors.affiliation: Institut für Mikrobiologie, Martin-Luther-Universität Halle, Halle, Germany, Kurt-Mothes-Str. 3, 06120 Halle, Germany.
authors.forename: Corinna
authors.initials: C
authors.lastname: Bleuel
authors.forename: Cornelia
authors.initials: C
authors.lastname: Grosse
authors.forename: Nadine
authors.initials: N
authors.lastname: Taudte
authors.forename: Judith
authors.initials: J
authors.lastname: Scherer
authors.forename: Dirk
authors.initials: D
authors.lastname: Wesenberg
authors.forename: Gerd J
authors.initials: GJ
authors.lastname: Krauss
authors.forename: Dietrich H
authors.initials: DH
authors.lastname: Nies
authors.forename: Gregor
authors.initials: G
authors.lastname: Grass
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004758:Enterobactin / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D007501:Iron / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009154:Mutation
chemical_list: D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D004758:Enterobactin; D029968:Escherichia coli Proteins; D007501:Iron; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C083496:AcrB protein, E coli; C477833:MdtF protein, E coli; C073126:tolC protein, E coli; C071960:acrF protein, E coli