Bacteria swim by rotating helical flagella

Slowed down 20 times

Turner et al., J. Bacteriol., 2000

...Powered by a molecular engine

Nakamura and Minamino, Biomolecules, 2019
Santiveri et al., Cell, 2020

Leake et al., Nature, 2006

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

How does the bacterial flagellar engine deal with changing loads?

We used electrorotation to control 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

Remodeling kinetics vary with electrorotation speed

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

Wadhwa et al., PNAS, 2019

Off-rate decreases with torque

The binding gets stronger at higher torque

A passive, biophysical mechanism of mechano-adaptation

Mechanosensitive remodeling is independent of the direction of rotation

Torque is the main parameter that governs stator remodeling

Wadhwa et al., BioRxiv, 2021

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

Cars and bacteria use different approaches

Cars adapt the transmission while bacteria adapt the engine itself

Take home

Bacterial motors adapt to changing loads by remodeling themselves.

Torque governs motor remodeling by tuning the binding kinetics.

Molecular machines are not static, fixed structures, but flexible, dynamic, and responsive.

References:
Wadhwa, Phillips, and Berg, 2019, PNAS 116: 11764-11769
Wadhwa, Tu, and Berg, 2021, bioRxiv 2021.01.19.427295

Acknowledgements

Collaborators
Howard Berg (Harvard)
Yuhai Tu (IBM)
Rob Phillips (Caltech)
Ethan Garner (Harvard)
Nicholas Taylor (U. Copenhagen)
Marc Erhardt (Humboldt U.)

K99/R00: GM134124