Measurement of Bacterial Flagella Force using Micromagnetic Tweezers*

Bacteria represent the most abundant group of organisms on the planet, serving as the foundation for ecosystems. A tail-like, spinning motor known as a flagellum drives their motion. Measuring and characterizing these flagella thrust forces, F_f, provides an opportunity to classify and probe some of the interesting bacterial swimming behaviors and to develop models for their hydrodynamics in different environments. In this study, magnetotactic bacteria, which are characterized by their innate magnetic properties, allows for controlling swimming behaviors with a combination of uniform external magnetic fields and local field gradients generated by micromagnets. By tuning the cell body orientation in the immediate vicinity of the micro magnets that yield well-characterized magnetic trapping forces, individual flagella thrust forces are non-invasively determined. The resulting measured forces are within an order of magnitude of previously reported values. Results based on this noninvasive micro magnetic tweezer-based approach to measure flagella thrust with relatively high accuracy for large numbers of individual cells will be presented. Potential applications under different chemical environments and spatial constraints will be discussed.