Scale invariance during bacterial reductive division observed by an extensive microperfusion system

In stable environments, cell size fluctuations are thought to be governed by simple physical principles, as suggested by recent finding of scaling properties. Here we show, using E. coli, that the scaling concept also rules cell size fluctuations under time-dependent conditions, even though the distribution changes with time. We develop a microfluidic device for observing dense and large bacterial populations, under uniform and switchable conditions. Triggering bacterial reductive division by switching to non-nutritious medium, we find that the cell size distribution changes in a specific manner that keeps its normalized form unchanged; in other words, scale invariance holds. This finding is underpinned by simulations of a model based on cell growth and intracellular replication. We also formulate the problem theoretically and propose a sufficient condition for the scale invariance. Our results emphasize the importance of intrinsic cellular replication processes in this problem, suggesting different distribution trends for bacteria and eukaryotes.