How bacteria can maximize forward speed or swimming efficiency with their flagella
DOI: 10.1063/10.0036554
How bacteria can maximize forward speed or swimming efficiency with their flagella lead image
The tail of a bacterial cell, known as a flagellum, allows the cell to propel itself through liquid. The flagellum is made of a hook, a basal body that acts as the motor, and a helical filament that experiences uneven force distribution during rotation.
Simulations by Liu et al. found that the hydrodynamic interactions between the cell body and its flagella can greatly affect thrust.
During swimming, the flagella create a flow that opposes the bacterial movement, while the flow field generated by the cell body aligns with this movement. When considering these hydrodynamic interactions in simulations, the authors found that they could increase the thrust generated by the flagella.
“Our research shows that there is an optimal flagellar morphology that maximizes either forward speed or swimming efficiency,” author Baopi Liu said.
They found that the optimal flagellar pitch angle for maximum forward speed is slightly lower than that for maximum swimming efficiency.
“This suggests that microswimmers possess the ability to fine-tune their pitch angle in response to varying ecological conditions,” Liu said.
Additionally, the results gave insight into why the flagellar Young’s modulus is relatively high. Young’s modulus is the property of a material which determines its stiffness.
“Research on bacterial motility advances not only microbiology and physics but also provides valuable insights into ecological functions,” Liu said. “Studying the motion mechanisms of single-flagellated bacteria can help us design more efficient and adaptable micro-robots for complex environments.”
Liu plans to conduct more simulations on bacterial swimming in complex environments, particularly the emergent behaviors in large populations.
Source: “Effects of flagellar morphology on swimming performance and directional control in microswimmers,” by Baopi Liu, Lu Chen, and Wenjun Xu, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0264456 .
