Kara-Ivanov M, Eisenbach M, Caplan S R
Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Biophys J. 1995 Jul;69(1):250-63. doi: 10.1016/S0006-3495(95)79896-4.
The purpose of this work was to study the changes in rotation rate of the bacterial motor and to try to discriminate between various sources of these changes with the aim of understanding the mechanism of force generation better. To this end Escherichia coli cells were tethered and videotaped with brief stroboscopic light flashes. The records were scanned by means of a computerized motion analysis system, yielding cell size, radius of rotation, and accumulated angle of rotation as functions of time for each cell selected. In conformity with previous studies, fluctuations in the rotation rate of the flagellar motor were invariably found. Employing an exclusively counterclockwise rotating mutant ("gutted" RP1091 strain) and using power spectral density, autocorrelation and residual mean square angle analysis, we found that a simple superposition of rotational diffusion on a steady rotary motion is insufficient to describe the observed rotation. We observed two additional rotational components, one fluctuating (0.04-0.6 s) and one oscillating (0.8-7 s). However, the effective rotational diffusion coefficient obtained after taking these two components into account generally exceeded that calculated from external friction by two orders of magnitude. This is consistent with a model incorporating association and dissociation of force-generating units.
这项工作的目的是研究细菌马达转速的变化，并试图区分这些变化的各种来源，以便更好地理解力产生的机制。为此，将大肠杆菌细胞固定并用短暂的频闪闪光进行录像。通过计算机化运动分析系统对记录进行扫描，得出所选每个细胞的细胞大小、旋转半径和旋转累积角度随时间的变化函数。与先前的研究一致，总是能发现鞭毛马达转速的波动。使用一种仅逆时针旋转的突变体（“缺失”RP1091菌株）并利用功率谱密度、自相关和剩余均方角分析，我们发现仅在稳定旋转运动上叠加旋转扩散不足以描述观察到的旋转。我们观察到另外两个旋转分量，一个是波动的（0.04 - 0.6秒），一个是振荡的（0.8 - 7秒）。然而，在考虑这两个分量后得到的有效旋转扩散系数通常比根据外部摩擦计算出的系数超出两个数量级。这与一个包含力产生单元的缔合和解离的模型一致。
