Simulating flagellated bacteria swimming

Understanding how bacteria swim propelled by flagella is important for disease pathogenesis and combating infections. Bacteria like E. coli self-propel within fluid environments through molecular motors that rotate helical flagella. Biomedical microrobots for drug delivery are being developed based on this transport mechanism.

Gauging this process through experimental and theoretical studies is difficult, because the hydrodynamics of such cells are complex. Therefore, developing versatile modelling is crucial.

Lee et al. present a computational model that deals with the complex aspects of bacterial flagellar movement. The researchers model a neutrally buoyant rigid body with helical elastic rod-like flagella to simulate the fluid-structure interaction previously neglected in research.

“The novel scheme presented for the cell body dynamics allows for the physically correct interaction of the cell body with motor-driven flexible flagella,” said author Sookkyung Lim. “Thus, we can apply this scheme to any free-swimming microorganisms propelled by flagella.”

The study demonstrates when flagella are bundled, the bundle thrusts the cell forward in a straight trajectory, while temporary flagellar unbundling allows the cell to change direction. The simulations show flagellar distribution and the angle between flagellar axes impacts this bundling.

The smaller the axial distance and angle between flagella, the greater the likelihood of bundle formation. These findings suggest cells with more flagella are more likely to form bundles, and the elastic property of flagella is vital for cell-fluid interaction.

“This model can be used to probe bacterial movement in various fluid environments,” said Lim. “We plan to investigate pathogen transport in the blood stream and provide design principles for bacteria-inspired microrobots that are maneuverable.”

Source: “A novel computational approach to simulate microswimmers propelled by bacterial flagella,” by Wanho Lee, Yongsam Kim, Charles S. Peskin and Sookkyung Lim. Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0069343 .