Robustness of Min protein system In vivo pattern formation on [MinE] vs. [MinD] phase space

The oscillation of the Min proteins represents one of the most striking dynamic pattern formations in biology. Despite its long history, some of the most fundamental aspects of the Min system remain unanswered. They are, (1) how many Min proteins do cells need to start oscillations? (2) Does the cell produce just enough Min proteins for oscillations or in excess? (3) How do the answers change under different growth conditions? In this work, we answer these questions by constructing a phase diagram in the MinD vs. MinE space, two key Min proteins required for the reaction-diffusion system. To this end, we engineered a E. coli strain to independently produce MinD and MinE using two inducible promoters, covering about two orders of magnitude dynamic range in concentrations. We find that the concentrations of Min proteins in the wildtype cells are close to the minimum concentrations, below which the system cannot sustain its oscillatory behavior. As we increased the concentration of MinD or MinE, we discovered various regimes such as standing wave, traveling wave, and their phase coexistence, in vivo. Our work, for the first time, shows how the biophysical properties of the Min proteins and the cellular physiology are intimately linked.