Nucleoid Segregation Dynamics and its Variability in Dividing and Filamentous E. Coli

Abstract

Segregation of the replicating chromosome from a single to two nucleoid bodies is one of the major processes in growing bacterial cells. It is tightly correlated with cell growth and division and this correlation is crucial for cell viability. The mechanism of segregation is still enigmatic: although it is believed that the underlying driving force is purely thermodynamic, it is obvious that the segregation dynamics is tuned by intricate interactions with other cellular processes. These interactions serve for flexibility in a changing environment and may possibly be the source of cell-to-cell phenotypic variability. We exploited the advantage of the chromosomally encoded HU-eGFP to monitor nucleoid segregation in live E. coli cells using time-lapse microscopy. The cells were grown in linear grooves formed in the agarose gel pad, convenient for the image processing of fluorescence intensity profiles along individual cell lineages. Analysis of these profiles produced nucleoid localization trajectories for each cell lineage and was used to obtain the main characteristics of the segregation process, namely, the start of partitioning, rates of separation and final positions, as well as variability of these characteristics throughout the population. Moreover, the same characteristics were determined for non-dividing, filamentous cells growing under the same conditions. Comparison between dividing and filamentous cells is aimed to reveal the involvement of physical boundaries and diffusion barriers in the control of nucleoid segregation dynamics. Our findings shed light on the role of these factors both in the mechanism of segregation and its variability in bacterial cells.