Thrust and Power Output of the Bacterial Flagellar Motor: A Micromagnetic Tweezers Approach

Abstract One of the most common swimming strategies employed by microorganisms is based on the use of rotating helical filaments, called flagella, that are powered by molecular motors. Determining the physical properties of this propulsive system is crucial to understanding the behavior of these organisms. Furthermore, the ability to dynamically monitor the activity of the flagellar motor is a valuable indicator of the overall energetics of the cell. In this work, inherently magnetic bacteria confined in micromagnetic CoFe traps are used to directly and non-invasively determine the flagellar thrust force and swimming speed of motile cells. The technique permits determination of the ratio of propulsive force to swimming speed (the hydrodynamic resistance) and the power output of the flagellar motor for individual cells over extended time periods. Cells subjected to UV radiation are observed to experience exponential decays in power output as a function of exposure time. By non-invasively measuring thrust, velocity and power output over time at a single cell level, this technique can serve as the foundation for fundamental studies of bacterial hydrodynamics and also provides a novel tether-free probe of single cell energetics over time.