Optimal swimming of multi-flagellated bacteria*

An important characteristic of motile multi-flagellated bacteria is their variable number of flagella, with some bacteria having only one, while others have a few dozen. The number of flagella in a cell is difficult to control in experiments, but it can be changed easily in simulations. This has motivated several theoretical investigations into the link between the swimming of bacteria and their number of flagella [1,2]. How does the number of flagella affect the swimming speed and efficiency of a bacterium? We revisit this open question using slender-body theory simulations, where we include the full hydrodynamic interactions inside a bundle of parallel helical filaments that rotate and translate in synchrony. In contrast to previous studies, we incorporate the full torque-speed relationship of the bacterial flagellar motor [3]. This enables us to obtain novel and surprising predictions on the swimming speed of multi-flagellated bacteria. Our observations are relevant to bacteria with a small number of flagella, such as the model organism Escherichia coli, and we hope will inspire new experiments to address this question.

 

[1] Kanehl, P. and Ishikawa, T. (2014). Phys. Rev. E, 89:042704

[2] Nguyen, F. T. M. and Graham, M. D. (2018). Phys. Rev. E, 98:042419

[3] Xing, J., Bai, F., Berry, R. M., and Oster, G. (2006). PNAS, 103:1260–1265