Replication-related control over cell division in Escherichia coli is growth-rate dependent

Abstract

How replication and division processes are coordinated in the cell cycle is a fundamental yet poorly understood question in cell biology. In Escherichia coli different data sets and models have supported a range of conclusions from one extreme where these two processes are tightly linked to another extreme where these processes are completely independent of each other. Using high throughput optical microscopy and cell cycle modeling, we show that in slow growth conditions replication and division processes are strongly correlated, indicating a significant coupling between replication and division. This coupling weakens as the growth rate of cells increases. Our data suggest that the underlying control mechanism in slow growth conditions is related to unreplicated chromosome blocking the onset of constriction at the midcell. We show that the nucleoid occlusion protein SlmA does not play a role in this process and neither do other known factors involved in positioning bacterial Z-ring relative to the chromosome. Altogether this work reconciles different ideas from the past and brings out a more nuanced role of replication in controlling the division process in a growth-rate dependent manner.

To bin or not to bin: analyzing single-cell growth data

“…For Figure 3B, Figure 3-figure supplements 2A-2D, 3A-3F, Figure 4-figure supplement 1D, the cell sizes are recorded within the cell cycle at equal intervals of 4 min, similar to that in the E. coli experiments of Ref. [32].…”

“…Slope of the best linear fit for ln( Table S2: The slope and the intercept of the best linear fit along with their 95% confidence intervals (CI) obtained on performing linear regression on experimental data. The data is collected for cells growing in M9 alanine, glycerol and glucose-cas media [32]. Simulations of the adder model for exponentially growing cells were carried out at multiple growth rates for N = 2500 cells.…”

“…L d vs L b plot was obtained using these cells and linear regression performed on it provided a best linear fit.Data from recent mother machine experiments on E. coli was used to make all other plots. Details are provided in Section 5.1 and Ref [32]…”

Two different cell-cycle processes determine the timing of cell division in Escherichia coli

“…Interestingly, when fitting our model to all datasets including our own, we found that p H ∼ 0.5 at slow growth (if the average doubling time is smaller than 1.4 h), while p H increases with decreasing doubling time. This trend is in qualitative agreement with recent work from Tiruvadi-Krishnan et al (2021 ), who propose that DNA replication limits division at slow growth but not at fast growth (see also Discussion). However, we note that part of this increase might also be caused by decreasing accuracy of detecting replication initiation during overlapping rounds of replication, which would artificially decrease correlations between replication and division.…”

“…However, at fast growth, p H seems to increase, based on fitting our model to data from Si et al (2019 ) (Figure 4 - Figure Supplement 3). While it is increasingly challenging to detect the time of initiation accurately in this regime, which could account for part of the increase of p H , support of this trend also comes from a recent study by Tiruvadi-Krishnan et al (2021 ). They demonstrate that temporal correlations between replication termination and z-ring constriction are high at slow growth, which supports a limiting role of DNA replication for cell division, but correlations decrease at fast growth, which then requires a different process to control cell division, in qualitative agreement with the concurrent-cycles model (Figure 4 - Figure Supplement 3).…”