Single-Cell Biophysics: Measurement, Modulation, and Modeling

Single-Cell Biophysics: Measurement, Modulation, and Modeling

Saturday Speaker Abstracts

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.