Single cells tell their own story: An updated framework for understanding stochastic variations in cell cycle progression in bacteria

Abstract

Our current understanding of the bacterial cell cycle is framed largely by population-based experiments that focus on the behavior of idealized average cells. Most famously, the contributions of Cooper and Helmstetter help to contextualize the phenomenon of overlapping replication cycles observed in rapidly growing bacteria. Despite the undeniable value of these approaches, their necessary reliance on the behavior of idealized average cells washes out the stochasticity inherent in single cell growth and physiology limiting their mechanistic value. To bridge this gap, we propose an updated and agnostic framework, informed by extant single-cell data, that quantitatively accounts for stochastic variations in single-cell dynamics and the impact of medium composition on cell growth and cell cycle progression. In this framework, stochastic timers sensitive to medium composition impact the relationship between cell cycle events, accounting for observed differences in the relationship between cell cycle events in slow and fast growing cells. We conclude with a roadmap for potential application of this framework to longstanding open questions in the bacterial cell cycle field.