Torque generated by the bacterial flagellar motor close to stall

Area of Science:

• Microbiology
• Biophysics

Background:

• Previous studies using electrorotation on Escherichia coli suggested a significant barrier to backward flagellar motor rotation.
• This barrier implied a higher torque requirement for backward motion compared to stopping the motor.

Purpose of the Study:

• To investigate the nature of the observed barrier to backward rotation in bacterial flagellar motors.
• To determine if the barrier is an intrinsic property of the motor or an artifact of experimental conditions.

Main Methods:

• Utilized electrorotation to apply controlled torque to tethered Escherichia coli cells.
• Analyzed the relationship between applied torque, motor speed, and direction of rotation.

Main Results:

• The barrier to backward rotation is primarily an artifact of angular variations in applied or motor torque.
• Bacterial flagellar motor torque is largely speed-independent or linearly dependent on speed in both forward and backward directions.
• Backward rotation can lead to catastrophic motor failure or reversible damage, indicated by slow recovery after electrorotation cessation.

Conclusions:

• The perceived barrier to backward flagellar motor rotation is an artifact and not an intrinsic property.
• While backward rotation is possible, it carries risks of motor damage, making it distinct from forward rotation.
• Existing interpretations of electrorotation experiments driving motors forward at high speeds remain valid.