Abrupt changes in flagellar rotation observed by laser dark-field microscopy.

Area of Science:

• Microbiology
• Biophysics
• Cellular Biology

Background:

• Bacteria like Escherichia coli and Salmonella typhimurium utilize rotary flagellar motors for motility.
• Previous studies on flagellar motor function were limited by low speeds under high-load conditions.
• High-speed, low-load analysis of single flagellar rotation with millisecond resolution is crucial for detailed motor function understanding.

Purpose of the Study:

• To develop and apply a novel technique for high-speed, low-load analysis of bacterial flagellar motor function.
• To investigate the dynamics of flagellar rotation, including speed, pauses, and reversals.
• To elucidate the role of the switch complex in flagellar motor operation.

Main Methods:

• Development of laser dark-field microscopy for high-speed (better than 1 ms temporal resolution) observation of single flagellar rotation.
• Analysis of flagellar rotation dynamics in Salmonella typhimurium.
• Comparison of wild-type and mutant strains with defects in the flagellar motor switch complex.

Main Results:

• Laser dark-field microscopy enables high-resolution analysis of flagellar motor function under low-load conditions.
• Salmonella typhimurium flagellar rotation is generally stable but exhibits occasional abrupt slowdowns, pauses, and reversals within 1 ms.
• Mutants with defects in the switch complex frequently showed altered rotation dynamics, indicating its importance in motor control.

Conclusions:

• The switch complex is critical for regulating flagellar motor direction, torque generation, and potentially motor speed.
• The developed laser dark-field microscopy technique provides unprecedented insight into the rapid dynamics of bacterial flagellar motors.
• Understanding flagellar motor function has implications for bacterial pathogenesis and the development of antimicrobial strategies.