Abstract
In stable environments, cell size fluctuations are thought to be governed by simple physical principles, as suggested by recent findings of scaling properties. Here, by developing a microfluidic device and using E. coli, we investigate the response of cell size fluctuations against starvation. By abruptly switching to non-nutritious medium, we find that the cell size distribution changes but satisfies scale invariance: the rescaled distribution is kept unchanged and determined by the growth condition before starvation. These findings are underpinned by a model based on cell growth and cell cycle. Further, we numerically determine the range of validity of the scale invariance over various characteristic times of the starvation process, and find the violation of the scale invariance for slow starvation. Our results, combined with theoretical arguments, suggest the relevance of the multifork replication, which helps retaining information of cell cycle states and may thus result in the scale invariance.
Highlights
In stable environments, cell size fluctuations are thought to be governed by simple physical principles, as suggested by recent findings of scaling properties
These findings suggest the existence of a statistical principle underlying the scale invariance, which is not influenced by details of the model
To understand what triggers the violation of the scale invariance, we focus on the state of the multifork replications, since our theory suggested the importance of the division rate, which is controlled by the state of the cell cycle
Summary
Cell size fluctuations are thought to be governed by simple physical principles, as suggested by recent findings of scaling properties. Scale invariance akin to Eq (1) was found for bacteria[5,6] for each cell age, and the function F( ⋅ ) was shown to be robust against changes in growth conditions, such as the temperature Those results, as well as theoretical models proposed in this context[1,7,8], have been obtained under steady environments, for which our understanding of single-cell growth statistics has been significantly deepened recently[9,10,11]. By contrast, it is unclear whether such a simple concept as scale invariance is valid under time-dependent conditions, where different regulations of cell cycle kinetics may come into play in response to environmental variations. We numerically show the range of validity of the scale invariance over various characteristic times of the starvation process, revealing that the number of multifork replications may be important for the scale invariance
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