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Single-Cell Biophysics: Measurement, Modulation, and Modeling
Saturday Speaker Abstracts
9
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.