Abstract

Mechanics plays an important role in cellular biology. Motile bacteria, for example, exploit the rotation of helical filaments to self-propel in fluids, and a critical number of mechanical processes are at the heart of their ability to swim and change direction. Here we focus on the rapid bundling and unbundling of helical flagellar filaments, an essential component to the run-and-tumble motion of bacteria equipped with many flagella, but whose physical mechanism is not yet fully understood. In this biolunch, I will discuss the helical geometry of bacterial flagella and the consequences it has for bacterial motility, namely for the freedom of bundling and the potential risk of tangling. Surprisingly, the mean number of flagella per bacterium observed in E. coli and S. typhimurium is very close to the threshold for tangle-free swimming predicted by our theoretical model. This and other findings lead us to the conclusion that the geometric properties of bacterial flagella are, in fact, well-suited for a life of constant bundling and unbundling, but luckily no tangling.