title: Theoretical results for chemotactic response and drift of E. coli in a weak attractant gradient.
abstract: The bacterium Escherichia coli (E. coli) moves in its natural environment in a series of straight runs, interrupted by tumbles which cause change of direction. It performs chemotaxis towards chemo-attractants by extending the duration of runs in the direction of the source. When there is a spatial gradient in the attractant concentration, this bias produces a drift velocity directed towards its source, whereas in a uniform concentration, E. coli adapts, almost perfectly in case of methyl aspartate. Recently, microfluidic experiments have measured the drift velocity of E. coli in precisely controlled attractant gradients, but no general theoretical expression for the same exists. With this motivation, we study an analytically soluble model here, based on the Barkai-Leibler model, originally introduced to explain the perfect adaptation. Rigorous mathematical expressions are obtained for the chemotactic response function and the drift velocity in the limit of weak gradients and under the assumption of completely random tumbles. The theoretical predictions compare favorably with experimental results, especially at high concentrations. We further show that the signal transduction network weakens the dependence of the drift on concentration, thus enhancing the range of sensitivity.
authors.affiliation: Department of Physics and Astrophysics, Delhi University, St. Stephen's College, Delhi 110007, India.
authors.forename: Melissa
authors.initials: M
authors.lastname: Reneaux
authors.forename: Manoj
authors.initials: M
authors.lastname: Gopalakrishnan
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000465:Algorithms; D001426:Bacterial Proteins / Q000378:metabolism; D002628:Chemoreceptor Cells / Q000378:metabolism; D002630:Chemotactic Factors / Q000494:pharmacology*; D002633:Chemotaxis / Q000502:physiology*; D004926:Escherichia coli / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000378:metabolism; D005407:Flagella / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D000072236:Methyl-Accepting Chemotaxis Proteins; D008745:Methylation / Q000187:drug effects; D008780:Methyltransferases / Q000378:metabolism; D008954:Models, Biological; D016202:N-Methylaspartate / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011956:Receptors, Cell Surface; D015398:Signal Transduction / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D002630:Chemotactic Factors; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D011956:Receptors, Cell Surface; C057331:Tar protein, E coli; C069656:CheB protein, Bacteria; D016202:N-Methylaspartate; C513923:CheR protein, E coli; D008780:Methyltransferases