Department of Physics, Ben-Gurion University of the Negev, Beer Sheva, Israel; The Ilse Katz Center for Nanotechnology, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Department of Physics, Ben-Gurion University of the Negev, Beer Sheva, Israel; Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Biophys J. 2021 Nov 16;120(22):5107-5123. doi: 10.1016/j.bpj.2021.10.004. Epub 2021 Oct 8.
Segregation of the replicating chromosome from a single to two nucleoid bodies is one of the major processes in growing bacterial cells. The segregation dynamics is tuned by intricate interactions with other cellular processes such as growth and division, ensuring flexibility in a changing environment. We hypothesize that the internal stochasticity of the segregation process may be the source of cell-to-cell phenotypic variability, in addition to the well-established gene expression noise and uneven partitioning of low copy number components. We compare dividing cell lineages with filamentous cells, where the lack of the diffusion barriers is expected to reduce the impact of other factors on the variability of nucleoid segregation dynamics. The nucleoid segregation was monitored using time-lapse microscopy in live E. coli cells grown in linear grooves. The main characteristics of the segregation process, namely, the synchrony of partitioning, rates of separation, and final positions, as well as the variability of these characteristics, were determined for dividing and filamentous lineages growing under the same conditions. Indeed, the gene expression noise was considerably homogenized along filaments as determined from the distribution of CFP and YFP stochastically expressed from the chromosome. We find that 1) the synchrony of nucleoid partitioning is progressively decreasing during consecutive cell cycles, but to a significantly lesser degree in filamentous than in dividing cells; 2) the mean partitioning rate of nucleoids is essentially the same in dividing and filamentous cells, displaying a substantial variability in both; and 3) nucleoids segregate to the same distances in dividing and filamentous cells. Variability in distances is increasing during successive cell cycles, but to a much lesser extent in filamentous cells. Our findings indicate that the variability of the chromosome segregation dynamics is reduced upon removal of boundaries between nucleoids, whereas the remaining variability is essentially inherent to the nucleoid itself.
染色体从单个核体分离到两个核体是细菌细胞生长过程中的主要过程之一。分离动力学通过与其他细胞过程（如生长和分裂）的复杂相互作用进行调节，确保了在不断变化的环境中的灵活性。我们假设，除了已经确立的基因表达噪声和低拷贝数成分的不均匀分配之外，分离过程的内部随机性可能是细胞间表型变异性的来源。我们将分裂细胞谱系与丝状细胞进行比较，其中扩散障碍的缺乏预计会降低其他因素对核体分离动力学变异性的影响。使用实时显微镜在生长在线性凹槽中的活大肠杆菌细胞中监测核体分离。确定了分离过程的主要特征，即分配的同步性、分离的速率以及最终位置，以及这些特征的可变性，这些特征是在相同条件下生长的分裂和丝状谱系的特征。确实，如从染色体随机表达的 CFP 和 YFP 的分布确定的那样，基因表达噪声沿着丝状细胞明显均匀化。我们发现：1）在连续的细胞周期中，核体分配的同步性逐渐降低，但在丝状细胞中比在分裂细胞中降低的程度要小得多；2）核体的平均分配速率在分裂和丝状细胞中基本相同，在两者中都表现出很大的可变性；3）核体在分裂和丝状细胞中分离到相同的距离。在连续的细胞周期中，距离的可变性增加，但在丝状细胞中增加的程度要小得多。我们的研究结果表明，去除核体之间的边界会降低染色体分离动力学的可变性，而剩余的可变性基本上是核体本身固有的。
