Hydrodynamic simulations of noncanonical flagellated bacteria

Hydrodynamic models of flagellar propulsion have been successful in reproducing and explaining many of the features of bacterial locomotion, such as the circular trajectories often observed under a microscope. The most common model for a bacterium is a rod-shaped or spheroidal cell body propelled by a single flagellum behind the cell and aligned with the long axis. Simulations taking into account the precise shape of the cell body and flagellum of a model swimmer show that these details strongly influence the hydrodynamic interaction between a swimmer and nearby surfaces. When the cell body is nearly spherical, there is a strong tendency to swim towards surfaces. The close proximity to the surface is expected to result in tight, circular trajectories. This is not consistent with observations of Magnetococcus marinus, which is an unusual bacterium in many ways. It is a magnetotactic bacterium that swims with two sheathed bundles of flagella located on the same side of its nearly spherical body. Using numerical simulations, we explore some generalizations of the canonical, monotrichous model to determine which features are important to the characteristic motion of microorganisms in the presence of flat surfaces.