Mechanisms and Dynamics of the Bacterial Flagellar Motor
Many bacteria are able to actively propel themselves through their complex environment, in search of resources and suitable niches. The source of this propulsion is the Bacterial Flagellar Motor (BFM), a molecular complex embedded in the bacterial membran
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Mechanisms and Dynamics of the Bacterial Flagellar Motor A. L. Nord and F. Pedaci
Abstract
Many bacteria are able to actively propel themselves through their complex environment, in search of resources and suitable niches. The source of this propulsion is the Bacterial Flagellar Motor (BFM), a molecular complex embedded in the bacterial membrane which rotates a flagellum. In this chapter we review the known physical mechanisms at work in the motor. The BFM shows a highly dynamic behavior in its power output, its structure, and in the stoichiometry of its components. Changes in speed, rotation direction, constituent protein conformations, and the number of constituent subunits are dynamically controlled in accordance to external chemical and mechanical cues. The mechano-sensitivity of the motor is likely related to the surface-sensing ability of bacteria, relevant in the initial stage of biofilm formation. Keywords
Bacterial flagellar motor · Bacterial motility · Biofilm · Chemosensing · Cooperativity · Ion motive force · Mechanosensing · Molecular motor · Protein exchange · Surface sensing A. L. Nord · F. Pedaci () Centre de Biochimie Structurale (CBS), INSERM, CNRS, University of Montpellier, Montpellier, France
Abbreviations BFM CW, CCW ECT FLIM FRAP GFP IMF MCP PG PMF SMF SNR TIRF
5.1
Bacterial Flagellar Motor Clock-Wise, Counter Clock-Wise Electron Cryotomography Fluorescence Loss in Photobleaching Fluorescence Recovery After Photobleaching Green Flourescent Protein Ion Motive Force Methyl-Accepting Chemoreceptor Protein Peptidoglycan Proton Motive Force Sodium Motive Force Signal to Noise Ratio Total Internal Reflection Fluorescence
Introduction
Active movement gives an important evolutionary advantage for survival, especially when embedded within a feedback loop which includes the ability to sense the environment and bias the displacement accordingly (Wei et al. 2011). Such directed movement in living systems appears even at the smallest scale, where many bacteria have evolved mechanisms to propel them-
© Springer Nature Switzerland AG 2020 G. Duménil, S. van Teeffelen (eds.), Physical Microbiology, Advances in Experimental Medicine and Biology 1267, https://doi.org/10.1007/978-3-030-46886-6_5
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selves, sense their environment, and control their displacement. This allows them to explore and find suitable niches in complex inhomogeneous environments. Since inertia plays a negligible role at the microscopic level (Purcell 1997), directed motion requires continuous energy consumption, and this is likely one reason why today we observe highly efficient molecular motors at work in living cells. Here we focus on a striking example of efficiency and power evolved to provide bacteria with motility: the rotary Bacterial Flagellar Motor (BFM). Found in many motile bacteria, the BFM is a large protein complex (∼11 MDa) in the membrane at the base of each flagellum. The BFM is one of the rare examples where rotation around an axis emerged in living systems, despite the requirem
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