title: Nonequivalence of membrane voltage and ion-gradient as driving forces for the bacterial flagellar motor at low load.
abstract: Many bacterial species swim using flagella. The flagellar motor couples ion flow across the cytoplasmic membrane to rotation. Ion flow is driven by both a membrane potential (V(m)) and a transmembrane concentration gradient. To investigate their relation to bacterial flagellar motor function we developed a fluorescence technique to measure V(m) in single cells, using the dye tetramethyl rhodamine methyl ester. We used a convolution model to determine the relationship between fluorescence intensity in images of cells and intracellular dye concentration, and calculated V(m) using the ratio of intracellular/extracellular dye concentration. We found V(m) = -140 +/- 14 mV in Escherichia coli at external pH 7.0 (pH(ex)), decreasing to -85 +/- 10 mV at pH(ex) 5.0. We also estimated the sodium-motive force (SMF) by combining single-cell measurements of V(m) and intracellular sodium concentration. We were able to vary the SMF between -187 +/- 15 mV and -53 +/- 15 mV by varying pH(ex) in the range 7.0-5.0 and extracellular sodium concentration in the range 1-85 mM. Rotation rates for 0.35-microm- and 1-microm-diameter beads attached to Na(+)-driven chimeric flagellar motors varied linearly with V(m). For the larger beads, the two components of the SMF were equivalent, whereas for smaller beads at a given SMF, the speed increased with sodium gradient and external sodium concentration.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, United Kingdom.
authors.forename: Chien-Jung
authors.initials: CJ
authors.lastname: Lo
authors.forename: Mark C
authors.initials: MC
authors.lastname: Leake
authors.forename: Teuta
authors.initials: T
authors.lastname: Pilizota
authors.forename: Richard M
authors.initials: RM
authors.lastname: Berry
mesh_terms: D003198:Computer Simulation; D004926:Escherichia coli / Q000502:physiology*; D005407:Flagella / Q000502:physiology*; D007477:Ions; D008564:Membrane Potentials / Q000502:physiology*; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology*; D009038:Motion; D009068:Movement / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D013314:Stress, Mechanical
chemical_list: D007477:Ions; D020409:Molecular Motor Proteins; D012964:Sodium