A new mode of swimming in singly flagellated .

SignificanceThe monotrichous was usually thought to swim in a pattern of "run and reverse" (possibly with pauses in between), where straight runs alternated with reverses with angular changes of swimming direction near 180°. Here, by simultaneously tracking the cell swimming and the morphology of its flagellum, we discovered a swimming mode in -the wrap mode, during which the flagellar filament wrapped around the cell body and induced large fluctuation of the body orientation. The wrap mode randomized swimming direction, resulting in a broad distribution of angular changes over 0 to 180° with a peak near 90°. This allowed the bacterium to explore the environment more efficiently, which we confirmed by stochastic simulations of chemotaxis.