Dielectrophoretic measurement of bacterial motor characteristics

Washizu, Masao; Kurahashi, Y.; Iochi, H.; Kurosawa, Osamu; Aizawa, Shin‐Ichi; Kudo, Satoshi; Magariyama, Yukio; Hotani, Hirokazu

doi:10.1109/28.216534

Cited by 72 publications

(53 citation statements)

References 17 publications

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“…The viscous load is smaller when motors turn flagellar filaments [55] or filament stubs attached to small spheres [56], and load can also be reduced by application of an external torque [15,57,58]. The rotation of such lightly loaded motors can be monitored by various light‐microscopic methods [55,56,59].…”

Section: Flagellar Motor Physiologymentioning

confidence: 99%

Flagellar movement driven by proton translocation

2003

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The bacterial £agellar motor couples ion £ow to rotary motion at high speed and with apparently ¢xed stoichiometry. The functional properties of the motor are quite well understood, but its molecular mechanism remains unknown. Recent studies of motor physiology, coupled with mutational and biochemical studies of the components, put signi¢cant constraints on the mechanism. Rotation is probably driven by conformational changes in membrane^protein complexes that form the stator. These conformational changes occur as protons move on and o¡ a critical Asp residue in the stator protein MotB, and the resulting forces are applied to the rotor protein FliG.

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Section: Flagellar Motor Physiologymentioning

confidence: 99%

Flagellar movement driven by proton translocation

2003

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“…Thus the bacterial motor force can be measured. In earlier work, positive DEP was used to estimate the force produced by the bacterial motor (6). However, that method was confounded by directional instability problems and is effective only when bacteria swim directly along the field lines.…”

Section: Introductionmentioning

confidence: 99%

Measurement of Bacterial Flagellar Thrust by Negative Dielectrophoresis

Hughes¹,

Morgan²

1999

Biotechnol. Prog.

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The force produced by the flagella of the bacterium Salmonella typhimurium has been measured using negative dielectrophoretic methods. The bacteria are held in a force funnel, produced using a non-uniform electric field. When the motor force is balanced against an opposing negative dielectrophoretic force the bacteria become motionless. Numerical simulations have been used to estimate the electric field gradient in the electrodes. Together with experimental observations of bacterial motion the data gives a value of the force produced by the bacterial motor to be 0.37pN.3

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“…This behavior is predicted by most models of the motor mechanism and cannot, therefore, be used to distinguish between them. The torque generated when the motor is forced to rotate against its natural direction provides more information and has been measured by using electrorotation (4,5). The latter authors (5) found a barrier to backwards rotation, i.e., that approximately twice as much torque was needed to make cells rotate backwards as was sufficient to stop them.…”

mentioning

confidence: 99%

Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers

Berry

Berg

1997

Proc. Natl. Acad. Sci. U.S.A.

132

102

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A cell of the bacterium Escherichia coli was tethered covalently to a glass coverslip by a single f lagellum, and its rotation was stopped by using optical tweezers. The tweezers acted directly on the cell body or indirectly, via a trapped polystyrene bead. The torque generated by the f lagellar motor was determined by measuring the displacement of the laser beam on a quadrant photodiode. The coverslip was mounted on a computer-controlled piezo-electric stage that moved the tether point in a circle around the center of the trap so that the speed of rotation of the motor could be varied. The motor generated Ϸ4500 pN nm of torque at all angles, regardless of whether it was stalled, allowed to rotate very slowly forwards, or driven very slowly backwards. This argues against models of motor function in which rotation is tightly coupled to proton transit and back-transport of protons is severely limited.Many species of bacteria swim with the aid of helical flagella that are powered at their base by a rotary motor embedded in the cell envelope. The power source for the motor is an electrochemical gradient of ions across the cytoplasmic membrane, the motor being a device for coupling rotation to ionic flux. These ions are either H ϩ (protons) or, in alkalophilic or marine bacteria, Na ϩ . In Escherichia coli, the motor can rotate in either direction, and cells navigate toward regions rich in nutrients by controlling this direction (1). Flagellar rotation traditionally has been measured by using the ''tethered cell'' assay, in which a single flagellum is attached to the surface, causing the cell body to counter-rotate (2). Whereas the flagella of swimming E. coli rotate at over 100 Hz and are difficult to observe directly, tethered cells rotate at Ϸ10 Hz and are comparatively easy to monitor.Measurement of the rotation rates of tethered cells and of flagellar bundles in swimming cells (3) established that the motor generates more torque under conditions of high load and low speed (tethered cells, or cells swimming in highly viscous media) than at low load and high speed (cells swimming in normal aqueous media). This behavior is predicted by most models of the motor mechanism and cannot, therefore, be used to distinguish between them. The torque generated when the motor is forced to rotate against its natural direction provides more information and has been measured by using electrorotation (4, 5). The latter authors (5) found a barrier to backwards rotation, i.e., that approximately twice as much torque was needed to make cells rotate backwards as was sufficient to stop them. This is predicted by some models of the motor mechanism, in particular those that include a stage in the torque-generating cycle in which the rotor and stator are tightly bound to each other, but not by others, for example those that generate torque by long range electrostatic interactions. However, further work using electrorotation suggested that the barrier to backwards rotation might be an artefact of that technique (6) arising from ang...

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Dielectrophoretic measurement of bacterial motor characteristics

Cited by 72 publications

References 17 publications

Flagellar movement driven by proton translocation

Flagellar movement driven by proton translocation

Measurement of Bacterial Flagellar Thrust by Negative Dielectrophoresis

Absence of a barrier to backwards rotation of the bacterial flagellar motor demonstrated with optical tweezers

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