Artwork: Dan Nowakowski/Nicholas Taylor
Autonomous mechano-adaptation in bacterial swimming motility
BPPB seminar
April 2022
Navish Wadhwa
Harvard University
slides for this talk: WadhwaLab.com/talks
Machines perform specific tasks for us
Cells use molecular machines to perform specific tasks
ATP synthase
Ribosome
Replisome
Do cells have smart machines too?
Yes, they do.
Many bacteria swim by rotating helical flagella
Slowed down 20X
A nanoscale motor powers
swimming in bacteria
How does the flagellar motor cope with changes in mechanical load?
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
What is the physical and molecular mechanism underlying this automatic gearshift?
How can we change motor load?
Instantaneously
Reversibly
Controllably
Electrorotation allows
full control over motor load
Instantaneous
Reversible
Controllable
Electrorotation allows
full control over motor load
A change in load triggers stepwise changes in motor speed
The motor adapts to changes
in load by remodeling its stator
Remodeling kinetics depend on electrorotation speed
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
The off-rate decreases with torque
Free energy of the bound state decreases with torque
The off-rate decreases exponentially with torque
Torque anisotropy allows us to test the model
Collapse of CCW and CW data validates the model
Molecular mechanism for torque-dependent unbinding rate
Low torque
High torque
Take home message
Future work: How do bacteria sense, process, and respond to their mechanical environment?
Openings for postdocs, gradaute students, technician, lab manager!
Acknowledgements
Howard C. Berg (1934 - 2021)
Rob Phillips (Caltech)
Yuhai Tu
(IBM)
Alberto Sassi (IBM)
