# Load-dependent adaptation near zero load in the bacterial flagellar motor

## TL;DR

This study introduces a novel method to measure stator unit dynamics in bacterial flagellar motors across various loads, revealing load-dependent adaptation mechanisms near zero load and advancing understanding of mechanosensing.

## Contribution

It presents a new technique to analyze stator dynamics at different loads, including near zero torque, enabling detailed study of load-dependent motor remodeling.

## Key findings

- Stator unit dynamics vary with external load.
- Motor speed and energy influence stator remodeling.
- Mechanosensing involves load-dependent stator assembly.

## Abstract

The bacterial flagellar motor is an ion-powered transmembrane protein complex which drives swimming in many bacterial species. The motor consists of a cytoplasmic 'rotor' ring and a number of 'stator' units, which are bound to the cell wall of the bacterium. Recently, it has been shown that the number of functional torque-generating stator units in the motor depends on the external load, and suggested that mechanosensing in the flagellar motor is driven via a 'catch bond' mechanism in the motor's stator units. We present a method that allows us to measure -- on a single motor -- stator unit dynamics across a large range of external loads, including near the zero-torque limit. By attaching superparamagnetic beads to the flagellar hook, we can control the motor's speed via a rotating magnetic field. We manipulate the motor to four different speed levels in two different ion-motive force (IMF) conditions. This framework allows for a deeper exploration into the mechanism behind load-dependent remodelling by separating out motor properties, such as rotation speed and energy availability in the form of IMF, that affect the motor torque.