Kudo S, Magariyama Y, Aizawa S
ERATO, Molecular Dynamic Assembly Project, Tsukuba, Japan.
Nature. 1990 Aug 16;346(6285):677-80. doi: 10.1038/346677a0.
Bacteria such as Escherichia coli and Salmonella typhimurium swim by rotating their flagella, each of which consists of an external helical filament and a rotary motor embedded in the cell surface. The function of the flagellar motor has been examined mainly by tethering the flagellar filament to a glass slide and observing the resultant rotation of the cell body. But under these conditions the motor operates at a very low speed (about 10 r.p.s.) owing to the unnaturally high load conditions inherent in this technique. Lowe et al. analysed the frequency of light scattered from swimming cells to estimate the average rotation speed of flagellar bundles of E. coli as about 270 r.p.s. To analyse motor function in more detail, however, measurement of high-speed rotation of a single flagellum (at low load) with a temporal resolution better than 1 ms is needed. We have now developed a new method--laser dark-field microscopy--which fulfils these requirements. We find that although the average rotation speed of S. typhimurium flagella is rather stable, there are occasional abrupt slowdowns, pauses and reversals (accomplished within 1 ms). These changes were frequently observed in mutants defective in one of the motor components (called the switch complex), suggesting that this component is important not only in switching rotational direction but also in torque generation or regulation.
诸如大肠杆菌和鼠伤寒沙门氏菌等细菌通过旋转其鞭毛来游动，每条鞭毛都由外部的螺旋状细丝和嵌入细胞表面的旋转马达组成。鞭毛马达的功能主要通过将鞭毛细丝系在载玻片上并观察细胞体随之产生的旋转来进行研究。但在这些条件下，由于该技术固有的异常高负载条件，马达以非常低的速度运行（约每秒10转）。洛维等人分析了从游动细胞散射的光的频率，以估计大肠杆菌鞭毛束的平均旋转速度约为每秒270转。然而，为了更详细地分析马达功能，需要测量单个鞭毛在低负载下的高速旋转，时间分辨率要优于1毫秒。我们现在开发了一种新方法——激光暗场显微镜——满足了这些要求。我们发现，虽然鼠伤寒沙门氏菌鞭毛的平均旋转速度相当稳定，但偶尔会出现突然减速、停顿和反转（在1毫秒内完成）。这些变化在马达的一个组件（称为开关复合体）有缺陷的突变体中经常观察到，这表明该组件不仅在切换旋转方向方面很重要，而且在扭矩产生或调节方面也很重要。
