(601g) Effect of Microstructure on the Wobbling Motion of a Bacterium

Bacteria like E.coli typically swim along helical trajectories in fluid media. This wobbling motion is due to the misalignment between the axes of their flagellar bundles and the spheroidal heads. Previous experiments on swimming bacteria in polymer solutions and colloidal suspensions have suggested that they swim with enhanced speeds in these media, which has been attributed to a reduction in the wobbling angle of the bacterium by the complex fluid medium. Motivated by this observation, we study the wobbling motion of a flagellated bacterium in a concentrated polymer solution numerically using a method that successfully combines slender body theory (for the flagellar bundle) and a finite different solver for the motion of the bacterium through the non-Newtonian fluid medium. To capture the effect of microstructure of the polymer solution, a two-fluid model, that allows for relative motion between the solvent and polymer is used, and the wobbling motion of a bacterium, caused by the misalignment of the axis of the flagellar bundle axis and the spheroidal head, is computed using this model. Using our simulations, we study the effect of the flagellar misalignment on the swimming speed of the bacterium in the polymer solution, and characterise the effect of microstructure and viscoelasticity on this motion. The results from our simulations are compared with previous experimental and numerical results, and shed light on the mechanism of wobbling motion of a bacterium in a complex fluid, which has several crucial applications.