Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Saturday Speaker Abstracts

The Tortoise and the Hare: Bacteria and Mitochondria Division Dynamics Revealed by Time-lapse Superresolution Microscopy Suliana Manley , Ambroise Lambert, Aster Vanhecke, Anna Archetti, Seamus Holden, Tatjana Kleele, Lina Carlini, Dora Mahecic. Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland. Bacteria and mitochondria share a common ancient evolutionary history, and their division processes involve a similar sequence of shape changes, before they pass through a singular point on their way to becoming two. Nonetheless, as bacteria and mitochondria divide, their composite envelopes are shaped by dramatically different constraints and forces. Bacteria control and maintain their size from generation to generation, using a mechanism of constant elongation per cell cycle. Mitochondria dynamically become fragmented or form fused networks, depending on their metabolic state and that of the cell. However, fundamental questions remain as to how the rates and timing of these processes are controlled. We are using superresolution microscopy, both structured illumination- and single molecule localization-based, to elucidate the physical mechanisms behind these dynamic processes. In the case of bacteria cell division, the control step for size homeostasis is unclear, and the relative roles of elongation and constriction and their coupling are poorly understood. Using genetic and pharmacological perturbations, we show that changing constriction rate alone can change the cell size. We also demonstrate that constriction duration compensates for elongation to allow for tighter homeostasis than either alone. We present a working model for how this may operate. In the case of mitochondrial fission, while the cellular and molecular components implicated are known, little is known about the role of physical constraints. By comparing successful fission events with reversal events, we identify the roles of different physical parameters, such as bending energy and external pulling forces. We use existing models for membrane fission to begin to build a toy physical model for mitochondrial fission.

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