Ko, WilliamLim, SookkyungLee, WanhoKim, YongsamBerg, HowardPeskin, Charles2019-10-112017Ko, William, Sookkyung Lim, Wanho Lee, Yongsam Kim, Howard C. Berg, and Charles S. Peskin. 2017. “Modeling Polymorphic Transformation of Rotating Bacterial Flagella in a Viscous Fluid.” Physical Review E 95 (6): 063106. https://doi.org/10.1103/PhysRevE.95.063106.1539-37551550-2376http://nrs.harvard.edu/urn-3:HUL.InstRepos:41534522The helical flagella that are attached to the cell body of bacteria such as Escherichia coli and Salmonella typhimurium allow the cell to swim in a fluid environment. These flagella are capable of polymorphic transformation in that they take on various helical shapes that differ in helical pitch, radius, and chirality. We present a mathematical model of a single flagellum described by Kirchhoff rod theory that is immersed in a fluid governed by Stokes equations. We perform numerical simulations to demonstrate two mechanisms by which polymorphic transformation can occur, as observed in experiments. First, we consider a flagellar filament attached to a rotary motor in which transformations are triggered by a reversal of the direction of motor rotation [L. Turner et al., J. Bacteriol. 182, 2793 (2000)]. We then consider a filament that is fixed on one end and immersed in an external fluid flow [H. Hotani, J. Mol. Biol. 156, 791 (1982)]. The detailed dynamics of the helical flagellum interacting with a viscous fluid is discussed and comparisons with experimental and theoretical results are provided.en-USJournal Article2019-10-1110.1103/PhysRevE.95.063106