Relative Rates of Surface and Volume Synthesis Set Bacterial Cell Size

Abstract

Summary Many studies have focused on the mechanisms underlying length and width determination in rod-shaped bacteria. Here, we focus instead on cell surface area to volume ratio (SA/V), and demonstrate that SA/V homeostasis underlies size determination. We propose a model whereby the instantaneous rates of surface and volume synthesis both scale with volume. This model predicts that these relative rates dictate SA/V and that cells approach a new steady-state SA/V exponentially, with a decay constant equal to the volume growth rate. To test this, we exposed diverse bacterial species to sublethal concentrations of a cell wall biosynthesis inhibitor and observed dose-dependent decreases in SA/V. Furthermore, this decrease was exponential and had the expected decay constant. The model also quantitatively describes SA/V alterations induced by other chemical, nutritional, and genetic perturbations. We additionally present evidence for a surface material accumulation threshold underlying division, sensitizing cell length to changes in SA/V requirements.

A Parallel Adder Coordinates Mycobacterial Cell-Cycle Progression and Cell-Size Homeostasis in the Context of Asymmetric Growth and Organization

“…We used time-lapse imaging to measure cell size and cell cycle timing in SSB-GFP M. smegmatis cells. Several studies recently developed a division adder model (also called an incremental model) of cell size control, in which bacteria add a constant length (Δ l bd ) from birth to division regardless of birth size (Figures 2A, S2D&S4; STAR Methods) [6, 8, 20–23]. Because Δ l bd is not correlated to birth length, we found that M. smegmatis is consistent with this aspect of the division adder model (Figure 2B) [4, 6, 19].…”

Is cell size a spandrel?

“…This scenario is referred to as the incremental or adder model. Recent work proposed a similar model, in which a constant surface area is added between birth and division (Harris and Theriot, 2016). Clearly, these models are different than Donachie’s – yet they both stem from empirical findings.…”

Invariance of Initiation Mass and Predictability of Cell Size in Escherichia coli

“…Recent studies have investigated the mechanism of cell size control via inhibition of biosynthesis [4,10]. When cells were exposed to sub-lethal dosage of a cell wall biosynthesis inhibitor, their surface-to-volume ratio changed to a new steady-state value in a dose-dependent manner [10].…”