Polymorphic transformation of helical flagella of bacteria.

Bacteria such as \textit{E. coli} swim in an aqueous environment by utilizing the rotation of flagellar motors and alternate two modes of motility, \textit{runs} and \textit{tumbles}. Runs are steady forward swimming driven by bundles of flagellar filaments whose motors are turning CCW; tumbles involve a reorientation of the direction of swimming triggered by motor reversals. During tumbling, the helical flagellum undergoes polymorphic transformations, which is a local change in helical pitch, helical radius, and handedness. In this work, we investigate the underlying mechanism of structural conformation and how this polymorphic transition plays a role in bacterial swimming.