Relative Rates of Surface and Volume Synthesis Set Bacterial Cell Size

• Maintenance of a condition-dependent surface area to volume ratio (SA/V) sets bacterial size
• Rates of volume and surface growth both scale with volume, producing SA/V homeostasis
• Biosynthesis of surface material in the cytoplasm links surface growth rate to volume
• A surface material accumulation threshold for division could underlie length control

SummaryMany 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.

Graphical AbstractFigure optionsDownload high-quality image (238 K)Download as PowerPoint slide