On torque and tumbling in swimming Escherichia coli
On torque and tumbling in swimming Escherichia coli
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DOI：
10.1128/jb.01501-06
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发表时间：
2007-03-01
影响因子：
3.2
通讯作者：
Berg, Howard C.
中科院分区：
文献类型：
--
作者：
Darnton, Nicholas C.;Turner, Linda;Berg, Howard C.
细菌通过旋转细长的螺旋丝来游动，每根螺旋丝的底部都由可逆旋转电机驱动。当周毛细胞的马达逆时针（CCW）转动时，它们的细丝形成束，驱动细胞前进。我们使用高速电荷耦合器件相机（500 帧/秒）对荧光标记的大肠杆菌细胞进行成像，并测量游泳速度、细胞体的旋转速率和鞭毛束的旋转速率。使用粘在玻璃上的细胞，我们研究了单个细丝，通过将细胞暴露在高强度光下来停止它们的旋转。根据这些测量结果，我们计算了束扭矩和推力以及主体扭矩和阻力的近似值，并估计了细丝刚度。对于固定细胞和游泳细胞，使用阻力理论估计的电机扭矩明显低于之前报道的电机扭矩。此外，一束多个鞭毛产生的扭矩比单个鞭毛产生的扭矩稍大。驱动单个灯丝的电机经常改变旋转方向。通常，但并非总是，这会导致细丝的旋向发生变化，细丝经历一系列多态性转变，从正常到半卷曲再到卷曲 I，然后，当电机再次逆时针旋转时，恢复到正常。电机反转是必要的，尽管并不总是足以引起灯丝手性的变化。具有相同旋向性的螺旋之间发生多态性转变，而所施加扭矩的符号没有变化。
Bacteria swim by rotating long thin helical filaments, each driven at its base by a reversible rotary motor. When the motors of peritrichous cells turn counterclockwise (CCW), their filaments form bundles that drive the cells forward. We imaged fluorescently labeled cells of Escherichia coli with a high-speed charge-coupled device camera (500 frames/s) and measured swimming speeds, rotation rates of cell bodies, and rotation rates of flagellar bundles. Using cells stuck to glass, we studied individual filaments, stopping their rotation by exposing the cells to high-intensity light. From these measurements we calculated approximate values for bundle torque and thrust and body torque and drag, and we estimated the filament stiffness. For both immobilized and swimming cells, the motor torque, as estimated using resistive force theory, was significantly lower than the motor torque reported previously. Also, a bundle of several flagella produced little more torque than a single flagellum produced. Motors driving individual filaments frequently changed directions of rotation. Usually, but not always, this led to a change in the handedness of the filament, which went through a sequence of polymorphic transformations, from normal to semicoiled to curly I and then, when the motor again spun CCW, back to normal. Motor reversals were necessary, although not always sufficient, to cause changes in filament chirality. Polymorphic transformations among helices having the same handedness occurred without changes in the sign of the applied torque.