The contribution of septal ring positioning proteins to cell size regulation in bacteria

Cell size is an important factor for survival that microorganisms tune to their environmental needs. Nevertheless, all microorganisms exhibit large heterogeneity in cell size even when experiencing homogenous environmental conditions. This heterogeneity is in part due to the stochastic nature of the complex processes that control cellular growth and division dynamics. It is also limited by cellular mechanisms that operate in concert to prevent size divergence over time. In this talk, I will discuss the contribution of one of these mechanisms, namely the Min proteins, to cell size regulation in the bacterial model organism E. coli. The Min proteins interactions and diffusion within the cell create oscillations along the cell’s length that aid in the formation of the septal ring at mid-cell. Previously, it was assumed that the Min proteins’ function is limited to the localization of the septal ring along the cell’s long axis. However, the dynamical pattern of these oscillations is sensitive to the cell length, which allows the Min proteins to coordinate the initiation time of the septal ring formation with the cell length and as a result can help regulate cell size. Our results reveal how the pattern of the Min proteins oscillations change with cell size and how that determines the timing of septal ring formation and ultimately cell size at subsequent divisions. The contribution of the Min proteins to cell size regulation is one that enables a cell born smaller than its sister during the “supposedly” symmetric division, to grow more and compensate for the size difference acquired during division. This ensures that cell size is tightly regulated and maintained within a physiologically viable range.