title: High binding affinity of repressor IolR avoids costs of untimely induction of myo-inositol utilization by Salmonella Typhimurium.
abstract: Growth of Salmonella enterica serovar Typhimurium strain 14028 with myo-inositol (MI) is characterized by a bistable phenotype that manifests with an extraordinarily long (34 h) and variable lag phase. When cells were pre-grown in minimal medium with MI, however, the lag phase shortened drastically to eight hours, and to six hours in the absence of the regulator IolR. To unravel the molecular mechanism behind this phenomenon, we investigated this repressor in more detail. Flow cytometry analysis of the iolR promoter at a single cell level demonstrated bistability of its transcriptional activation. Electrophoretic mobility shift assays were used to narrow the potential binding region of IolR and identified at least two binding sites in most iol gene promoters. Surface plasmon resonance spectroscopy quantified IolR binding and indicated its putative oligomerization and high binding affinity towards specific iol gene promoters. In competitive assays, the iolR deletion mutant, in which iol gene repression is abolished, showed a severe growth disadvantage of ~15% relative to the parental strain in rich medium. We hypothesize that the strong repression of iol gene transcription is required to maintain a balance between metabolic flexibility and fitness costs, which follow the inopportune induction of an unusual metabolic pathway.
authors.affiliation: Lehrstuhl für Mikrobielle Ökologie, Zentralinstitut für Ernährungs- und Lebensmittelforschung ZIEL, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, Germany.
authors.forename: Jessica
authors.initials: J
authors.lastname: Hellinckx
authors.affiliation: Biozentrum, Bereich Mikrobiologie, Ludwig-Maximilians-Universität München, Großhaderner Str. 2-4, 82152 Martinsried/München, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Heermann
authors.affiliation: Lehrstuhl für Mikrobielle Ökologie, Zentralinstitut für Ernährungs- und Lebensmittelforschung ZIEL, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, Germany.
authors.forename: Angela
authors.initials: A
authors.lastname: Felsl
authors.affiliation: Lehrstuhl für Mikrobielle Ökologie, Zentralinstitut für Ernährungs- und Lebensmittelforschung ZIEL, Technische Universität München, Weihenstephaner Berg 3, 85354 Freising, Germany.|Friedrich-Loeffler-Institut, Institut für Molekulare Pathogenese, Naumburger Str. 96a, 07743 Jena, Germany.
authors.forename: Thilo M
authors.initials: TM
authors.lastname: Fuchs
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D003001:Cloning, Molecular; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D005822:Genetic Vectors / Q000737:chemistry / Q000378:metabolism; D007294:Inositol / Q000378:metabolism / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D020349:Surface Plasmon Resonance; D015533:Transcriptional Activation
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D011994:Recombinant Proteins; D012097:Repressor Proteins; D007294:Inositol