Skarstad K, Steen H B, Boye E
J Bacteriol. 1985 Aug;163(2):661-8. doi: 10.1128/jb.163.2.661-668.1985.
A computer simulation routine has been made to calculate the DNA distributions of exponentially growing cultures of Escherichia coli. Calculations were based on a previously published model (S. Cooper and C.E. Helmstetter, J. Mol. Biol. 31:519-540, 1968). Simulated distributions were compared with experimental DNA distributions (histograms) recorded by flow cytometry. Cell cycle parameters were determined by varying the parameters to find the best fit of theoretical to experimental histograms. A culture of E. coli B/r A with a doubling time of 27 min was found to have a DNA replication period (C) of 43 min and an average postreplication period (D) of 22 to 23 min. Similar cell cycle parameters were found for a 60-min B/r A culture. Initiations of DNA replication at multiple origins in one and the same cell were shown to be essentially synchronous. A slowly growing B/r A culture (doubling time, 5.5 h) had an average prereplication period (B) of 2.3 h; C = 2.4 h and D = 0.8 h. It was concluded the the C period has a constant duration of 43 min (at 37 degrees C) at fast growth rates (doubling times, less than 1 h) but increases at slow growth rates. Thus, our results obtained with unperturbed exponential cultures in steady state support the model of Cooper and Helmstetter which was based on data obtained with synchronized cells.
已编制了一个计算机模拟程序来计算大肠杆菌指数生长培养物的DNA分布。计算基于先前发表的模型（S. 库珀和C.E. 赫尔姆斯泰特，《分子生物学杂志》31:519 - 540，1968年）。将模拟分布与通过流式细胞术记录的实验DNA分布（直方图）进行比较。通过改变参数来确定细胞周期参数，以找到理论直方图与实验直方图的最佳拟合。发现倍增时间为27分钟的大肠杆菌B/r A培养物的DNA复制期（C）为43分钟，复制后期平均持续时间（D）为22至23分钟。对于60分钟的B/r A培养物，发现了类似的细胞周期参数。显示在同一个细胞中的多个复制起点处的DNA复制起始基本上是同步的。一个生长缓慢的B/r A培养物（倍增时间为5.5小时）的复制前期平均持续时间（B）为2.3小时；C = 2.4小时，D = 0.8小时。得出的结论是在快速生长速率（倍增时间小于1小时）下，C期在37摄氏度时具有43分钟的恒定持续时间，但在生长缓慢时会增加。因此，我们在稳态下未受干扰的指数培养物中获得的结果支持了基于同步细胞数据的库珀和赫尔姆斯泰特模型。
