Threshold accumulation of a constitutive protein explainsE. colicell division behavior in nutrient upshifts

Abstract

Despite of a boost of recent progress in dynamic single-cell measurements and analyses in E. coli, we still lack a mechanistic understanding of the determinants of the decision to divide. Specifically, the debate is open regarding the hierarchy of processes linking growth and chromosome replication to division, and on the molecular origin of the observed "adder correlations", whereby cells divide adding roughly a constant volume independent of their initial volume. In order to gain insight into these questions, we interrogate dynamic size-growth behavior of single cells across nutrient upshifts with a high-precision microfluidic device. We find that the division rate changes quickly after nutrients change, much before growth rate goes to a steady state, and in a way that adder correlations are robustly conserved. Comparison of these data to simple mathematical models falsifies proposed mechanisms where replication-segregation or septum completion are the limiting step for cell division. Instead, we show that the accumulation of a putative constitutively expressed "P-sector divisor" protein explains the behavior during the shift.

Multiple timescales in bacterial growth homeostasis

“…In motor learning, the significance of such null-directions was implicated in acquiring novel capabilities while keeping functional structures intact (Perich, Gallego, and Miller 2018). Indication of a possible analogous role for our system is suggested by recent results on transitions between external conditions (Panlilio et al 2020); this possibility calls for further investigation.…”

“…With symmetric cell division, this would dictate that cells roughly double their size over the cell-cycle. This, in turn, requires the set-points (time-averages) of growth-rate and inter-division time to be correlated within each lineage, so that α τ ≈ ln 2; Fig.3C(blue circles) shows that indeed the set-points are located along this expected line (black dashed line).Correlations between growth-rate and inter-division time were previously reported over short-times, on a cycle-by-cycle basis(Grilli et al 2018;Panlilio et al 2020). Typically such correlations are inferred from a large number of data points, each representing a single cell-cycle from the pooled ensemble, making up a noisy cloud; in our experiments, this set of points has a Pearson correlation coefficient of ρ = −0.52.…”

“…However in the short-term, cell size clearly couples to growth within a cell-cycle. For example, recent work has shown that certain discrete events related to division depend on threshold accumulation of specific proteins, whose production is in turn dependent on cell size (Nordholt, Heerden, and Bruggeman 2020;Panlilio et al 2020;Si et al 2020). In other publications growth-rate was reported to compensate, within a single cycle, for noise that occurs at division (Vashistha, Kohram, and Salman 2021;Nordholt, Heerden, and Bruggeman 2020;Kohram et al 2021).…”

“…Finally, it appears that there is a limit on the amount of information one can draw from observing statistical properties in steady-state balanced growth, since steady-state statistics can be consistent with alternative underlying mechanisms. Indeed, recent work that examined single-cell transient dynamics between different environments (Panlilio et al 2020) was able to distinguish between different mechanisms and to rule out some scenarios that are inconsistent with dynamic data.…”

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

“…Recent theoretical work supports this relationship(Serbanescu et al, 2020) based on the assumption of constitutive divisor expression. The same assumption also finds some experimental validation from nutrient-shift data(Panlilio et al, 2020).…”