Cell size regulation induces sustained oscillations in the population growth rate

There are negative correlations between the generation time of a biological cell and those of its descendants. If a cell grows for a longer time than expected, its daughter cells will be larger at birth and have to compensate for their sizes by dividing slightly earlier than expected. Otherwise, the noise in the generation times would accumulate over generations in the size of the cells, leading to extremely large cells. This process is known as cell size control. In this talk, I discuss the effect of these correlations on the dynamics of population growth of microorganisms. I show that any non-zero correlation that is due to cell-size control can induce long-term oscillations in the population growth rate. The population only reaches its steady state due to the often-neglected variability in the growth rates of individual cells. The relaxation time scale of the population to its steady state is determined from the distribution of single-cell growth rates independent of the details of the division process or the cell-size regulation. I propose an experimental method to measure single-cell growth variability by observing how long it takes for the population to reach its steady state, a measurement that is significantly easier and less biased than single-cell measurements.