Many bacteria swim by rotating helical flagella

Slowed down 20 times

Turner et al., J. Bacteriol., 2000

Reversal of flagellar rotation enables changes in the swimming direction

Turner et al., J. Bacteriol., 2000

A nanoscale motor powers flagellar rotation

Nakamura and Minamino, Biomolecules, 2019

Leake et al., Nature, 2006

Santiveri et al., Cell, 2020
Deme et al., Nat. Microbiol., 2020

Torque production differs between CCW and CW

Chen and Berg, Biophys. J., 2000
Yuan et al, PNAS, 2010

Automatic gearshift in cars allows the engine to adapt to changing terrains

Automatic gearshift in E. coli allows the motor to adapt to changing loads

Lele et al., PNAS, 2013

What is the physical and molecular mechanism underlying this automatic gearshift?

How can we change motor load?

Electrorotation allows full control on motor load

Electrorotation allows full control on motor load

A change in load triggers stepwise changes in motor speed

Wadhwa et al., PNAS, 2019

The stator remodels in response to load change

Wadhwa et al., PNAS, 2019
Lele et al., PNAS, 2013
Nord et al., PNAS, 2017

Remodeling kinetics vary with electrorotation speed

Wadhwa et al., PNAS, 2019

Higher electrorotation speed leads to lower torque

Hypothesis
Stator remodeling depends on torque

A quantitative model for stator assembly

We extracted the on rate ($k_+$) and the off rate ($k_-$) from the data

Wadhwa et al., PNAS, 2019

The off-rate decreases with torque

Free energy of the bound state decreases with torque

The off-rate decreases exponentially with torque

Molecular mechanism for torque-dependent unbinding rate

Low torque

High torque

Torque anisotropy allows us to test the model

Collapse of CCW and CW data validates the model

Wadhwa et al., PNAS, 2021

Conclusions and perspective

Cars and bacteria use different approaches

Cars adapt the transmission while bacteria adapt the engine itself

Acknowledgements