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Tuning the torque-speed characteristics of the bacterial flagellar motor to enhance swimming speed

Prakash, P and Abdulla, AZ and Singh, V and Varma, M (2019) Tuning the torque-speed characteristics of the bacterial flagellar motor to enhance swimming speed. In: Physical Review E, 100 (6).

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Official URL: http://dx.doi.org/10.1103/PhysRevE.100.062609


In a classic paper, Purcell Proc. Natl. Acad. Sci. U. S. A. 94, 11307 (1997)10.1073/pnas.94.21.11307 analyzed the dynamics of flagellated bacterial swimmers and derived a geometrical relationship which maximizes the propulsion efficiency. Experimental measurements for wild-type bacterial species E. coli have revealed that they closely satisfy this geometric optimality. However, dependence of the flagellar motor speed on the load and more generally the role of the torque-speed characteristics of the flagellar motor are not considered in Purcell's original analysis. Here we derive a tuned condition representing a match between the flagella geometry and the torque-speed characteristics of the flagellar motor to maximize the bacterial swimming speed for a given load. This condition is independent of the geometric optimality condition derived by Purcell. Interestingly, this condition is not satisfied by wild-type E. coli which swims 2-3 times slower than the maximum possible speed given the amount of available motor torque. Finally, we present experimental data on swimming dynamics of a cargo laden bacterial system which follows our analytical model. Our analysis also reveals the existence of an anomalous propulsion regime where the swim speed increases with increasing load (drag).

Item Type: Journal Article
Publication: Physical Review E
Publisher: American Physical Society
Additional Information: Copyright of this article belongs to American Physical Society
Keywords: Escherichia coli; Geometry; Mutagenesis; Propulsion; Torque, Bacterial flagellar; Bacterial species; Bacterial systems; Flagellar motors; Geometrical relationship; Optimality conditions; Propulsion efficiency; Torque speed characteristic, Speed, article; controlled study; flagellum; geometry; human; swimming speed; torque; wild type
Department/Centre: Division of Biological Sciences > Molecular Reproduction, Development & Genetics
Division of Interdisciplinary Sciences > Robert Bosch Centre for Cyber Physical Systems
Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 18 Feb 2020 10:17
Last Modified: 28 Aug 2022 05:39
URI: https://eprints.iisc.ac.in/id/eprint/64555

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