Mechanobiology Institute, National University of Singapore, Singapore, Singapore.
Appl Environ Microbiol. 2013 Aug;79(15):4734-43. doi: 10.1128/AEM.01027-13. Epub 2013 May 31.
We have developed a program that can accurately analyze the dynamic properties of tethered bacterial cells. The program works especially well with cells that tend to give rise to unstable rotations, such as polar-flagellated bacteria. The program has two novel components. The first dynamically adjusts the center of the cell's rotational trajectories. The second applies piecewise linear approximation to the accumulated rotation curve to reduce noise and separate the motion of bacteria into phases. Thus, it can separate counterclockwise (CCW) and clockwise (CW) rotations distinctly and measure rotational speed accurately. Using this program, we analyzed the properties of tethered Pseudomonas aeruginosa and Pseudomonas putida cells for the first time. We found that the Pseudomonas flagellar motor spends equal time in both CCW and CW phases and that it rotates with the same speed in both phases. In addition, we discovered that the cell body can remain stationary for short periods of time, leading to the existence of a third phase of the flagellar motor which we call "pause." In addition, P. aeruginosa cells adopt longer run lengths, fewer pause frequencies, and shorter pause durations as part of their chemotactic response. We propose that one purpose of the pause phase is to allow the cells to turn at a large angle, where we show that pause durations in free-swimming cells positively correlate with turn angle sizes. Taken together, our results suggest a new "run-reverse-turn" paradigm for polar-flagellated Pseudomonas motility that is different from the "run-and-tumble" paradigm established for peritrichous Escherichia coli.
我们开发了一个程序，可以准确地分析系绳细菌细胞的动态特性。该程序特别适用于容易产生不稳定旋转的细胞，例如极鞭毛细菌。该程序有两个新颖的组件。第一个组件动态地调整细胞旋转轨迹的中心。第二个组件将累积的旋转曲线分段线性逼近，以减少噪声并将细菌的运动分为不同的阶段。因此，它可以将逆时针（CCW）和顺时针（CW）旋转明显区分开来，并准确测量旋转速度。使用该程序，我们首次分析了系绳铜绿假单胞菌和恶臭假单胞菌细胞的特性。我们发现，假单胞菌鞭毛马达在 CCW 和 CW 阶段花费相同的时间，并且在两个阶段以相同的速度旋转。此外，我们发现细胞体可以短时间保持静止，导致鞭毛马达存在我们称之为“暂停”的第三阶段。此外，铜绿假单胞菌细胞作为其趋化反应的一部分，采用更长的运行长度、更少的暂停频率和更短的暂停持续时间。我们提出暂停阶段的一个目的是允许细胞以大角度旋转，我们表明自由泳细胞中的暂停持续时间与转弯角度大小呈正相关。总之，我们的结果表明，极性鞭毛假单胞菌运动的新“运行-反转-转弯”范例与为周毛大肠杆菌建立的“运行-翻滚”范例不同。
