Cell size regulation induces sustained oscillations in the population growth rate

TL;DR

This paper demonstrates that cell-size regulation causes persistent oscillations in microbial population growth rates, with the relaxation time governed by single-cell growth variability, validated through experimental data.

Contribution

It reveals that even minimal correlations from cell-size regulation induce sustained oscillations and identifies growth rate variability as key to population stabilization.

Findings

Correlations due to cell-size regulation cause long-term oscillations.

Population reaches steady state only when growth rate variability is included.

Relaxation time depends on single-cell growth rate distribution, not division noise.

Abstract

We study the effect of correlations in generation times on the dynamics of population growth of microorganisms. We show that any non-zero correlation that is due to cell-size regulation, no matter how small, induces long-term oscillations in the population growth rate. The population only reaches its steady state when we include the often-neglected variability in the growth rates of individual cells. We discover that the relaxation time scale of the population to its steady state is determined by the distribution of single-cell growth rates and is surprisingly independent of details of the division process such as the noise in the timing of division and the mechanism of cell-size regulation. We validate the predictions of our model using existing experimental data and propose an experimental method to measure single-cell growth variability by observing how long it takes for the population to reach its steady state or balanced growth.