Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Phys Biol. 2011 Dec;8(6):066003. doi: 10.1088/1478-3975/8/6/066003. Epub 2011 Oct 21.
Bacterial cell division takes place in three phases: Z-ring formation at midcell, followed by divisome assembly and building of the septum per se. Using time-lapse microscopy of live bacteria and a high-precision cell edge detection method, we have previously found the true time for the onset of septation, τ(c), and the time between consecutive divisions, τ(g). Here, we combine the above method with measuring the dynamics of the FtsZ-GFP distribution in individual Escherichia coli cells to determine the Z-ring positioning time, τ(z). To analyze the FtsZ-GFP distribution along the cell, we used the integral fluorescence profile (IFP), which was obtained by integrating the fluorescence intensity across the cell width. We showed that the IFP may be approximated by an exponential peak and followed the peak evolution throughout the cell cycle, to find a quantitative criterion for the positioning of the Z-ring and hence the value of τ(z). We defined τ(z) as the transition from oscillatory to stable behavior of the mean IFP position. This criterion was corroborated by comparison of the experimental results to a theoretical model for the FtsZ dynamics, driven by Min oscillations. We found that τ(z) < τ(c) for all the cells that were analyzed. Moreover, our data suggested that τ(z) is independent of τ(c), τ(g) and the cell length at birth, L(0). These results are consistent with the current understanding of the Z-ring positioning and cell septation processes.
在细胞中部形成 Z 环，然后是分裂体的组装和隔膜的形成。通过对活细菌进行延时显微镜观察和高精度细胞边缘检测方法，我们之前已经找到了隔膜形成的真正时间 τ(c) 和连续分裂之间的时间 τ(g)。在这里，我们将上述方法与测量单个大肠杆菌细胞中 FtsZ-GFP 分布的动力学相结合，以确定 Z 环定位时间 τ(z)。为了分析 FtsZ-GFP 沿细胞的分布，我们使用了积分荧光分布 (IFP)，该分布通过沿细胞宽度积分荧光强度来获得。我们表明，IFP 可以用指数峰近似，并且在整个细胞周期中跟随峰的演化，从而找到 Z 环定位的定量标准，从而确定 τ(z)的值。我们将 τ(z)定义为平均 IFP 位置的振荡到稳定行为的转变。该标准通过将实验结果与 Min 振荡驱动的 FtsZ 动力学的理论模型进行比较得到了证实。我们发现，对于所有分析的细胞，τ(z) < τ(c)。此外，我们的数据表明，τ(z)与 τ(c)、τ(g)和出生时的细胞长度 L(0)无关。这些结果与当前对 Z 环定位和细胞分裂过程的理解一致。
