Single-Cell Biophysics: Measurement, Modulation, and Modeling
Saturday Speaker Abstracts
14
Stator Stoichiometry and Mechanosensitivity of the Bacterial Flagellar Motor Probed by
Load Manipulation
Ashley L. Nord
, Emily Gachon, Alessandro Barducci, Francesco Pedaci.
Centre de Biochimie Structurale, Montpellier, France.
The bacterial flagellar motor (BFM) is the multi-component complex which powers the
swimming and swarming of many motile bacteria. The BFM structure, many details of which are
still unknown, displays a rich dynamic behavior in terms of exchange and conformational change
of its internal components. The torque of this rotary motor is provided by stators, ion motive
force powered ion channels which are known to assemble and disassemble dynamically in the
BFM. Recently, it has been observed that this turn-over is mechano-sensitive, with the number of
engaged stators dependent upon the external load acting on the motor. Despite their central role
in the function of the BFM, a systematic study of the stator dynamics, as a function of the
external parameters in unperturbed motors, is lacking. Here we provide a quantitative and non-
invasive measurement of the temporal behavior of the stators active in the BFM of
E. coli
, by
estimating stator stoichiometry from high-resolution single-motor torque traces, quantifying for
the first time the dependence between stator number and external load at steady-state.
Furthermore, a rapid and controlled change in the external load, applied via a magnetic field,
allows us to directly probe BFM mechano-sensitivity, systematically triggering and detecting
stator association and dissociation. We incorporate these results into an adsorption model of
stator kinetics, providing the first step into understanding the mechanism of mechano-sensitivity
of the BFM.