Helical motion of the cell body enhances
            <i>Caulobacter crescentus</i>
            motility

Liu, Bin; Gulino, Marco; Morse, Michael; Tang, Jay X.; Breuer, Kenneth S.

doi:10.1073/pnas.1407636111

Cited by 81 publications

(85 citation statements)

References 20 publications

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“…This buckling manifests only as a brief trajectory ''flick,'' as the hook winds up again and stiffens, realigning the swimmer (3). Further evidence of buckling was inferred by Liu et al (7) from the helical trajectories of Caulobacter crescentus, caused by consistent propulsion off-axis to the cell body.…”

Section: Introductionmentioning

confidence: 93%

Buckling Instabilities and Complex Trajectories in a Simple Model of Uniflagellar Bacteria

Nguyen

Graham

2017

Biophysical Journal

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Observations of uniflagellar bacteria show that buckling instabilities of the hook protein connecting the cell body and flagellum play a role in locomotion. To understand this phenomenon, we develop models at varying levels of description with a particular focus on the parameter dependence of the buckling instability. A key dimensionless group called the flexibility number measures the hook flexibility relative to the thrust exerted by the flagellum; this parameter and the geometric parameters of the cell determine the stability of straight swimming. Two very simple models amenable to analytical treatment are developed to examine buckling in stationary (pinned) and moving swimmers. We then consider a more detailed model incorporating a helical flagellum and the rotational degrees of freedom of the cell body and flagellum, and we use numerical simulations to map out the parameter dependence of the buckling instability. In all models, a bifurcation occurs as the flexibility number increases, separating equilibrium configurations into straight or bent, and for the full model, separating trajectories into straight or helical. More specifically for the latter, the critical flexibility marks the transition from periodicity to quasi-periodicity in the behavior of variables determining configuration. We also find that for a given body geometry, there is a specific flagellar geometry that minimizes the critical flexibility number at which buckling occurs. These results highlight the role of flexibility in the biology of real organisms and the engineering of artificial microswimmers.

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Section: Introductionmentioning

confidence: 93%

Buckling Instabilities and Complex Trajectories in a Simple Model of Uniflagellar Bacteria

Nguyen

Graham

2017

Biophysical Journal

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“…Even during a run, the bacterium deviates from a straight path due to imperfections in the flagellar bundle, and the resulting small-amplitude orientation fluctuations, resemble a rotary diffusion process (Berg 1993;. The run-and-tumble motility paradigm applies to other micro-scale swimmers including other bacteria, both uniflagellated (C. crescentus; Liu et al 2014) and peritrichously flagellated (B. subtilis; Rao, Kirby & Arkin 2004, S. typhimurium;Stocker 2011) ones, and eukaryotes (C. reinhardtii; Polin et al 2009), although the underlying mechanisms for the tumble events are varied. In what follows, swimmers which lack any intrinsic orientation relaxation mechanisms, and only change their orientation due to hydrodynamic interactions, as in the simulations quoted above, are termed straight swimmers.…”

Section: Introductionmentioning

confidence: 99%

Collective motion in a suspension of micro-swimmers that run-and-tumble and rotary diffuse

Krishnamurthy

Subramanian

2015

J. Fluid Mech.

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Recent experiments have shown that suspensions of swimming micro-organisms are characterized by complex dynamics involving enhanced swimming speeds, large-scale correlated motions and enhanced diffusivities of embedded tracer particles. Understanding this dynamics is of fundamental interest and also has relevance to biological systems. The observed collective dynamics has been interpreted as the onset of a hydrodynamic instability, of the quiescent isotropic state of pushers, swimmers with extensile force dipoles, above a critical threshold proportional to the swimmer concentration. In this work, we develop a particle-based model to simulate a suspension of hydrodynamically interacting rod-like swimmers to estimate this threshold. Unlike earlier simulations, the velocity disturbance field due to each swimmer is specified in terms of the intrinsic swimmer stress alone, as per viscous slender-body theory. This allows for a computationally efficient kinematic simulation where the interaction law between swimmers is known a priori. The neglect of induced stresses is of secondary importance since the aforementioned instability arises solely due to the intrinsic swimmer force dipoles.Our kinematic simulations include, for the first time, intrinsic decorrelation mechanisms found in bacteria, such as tumbling and rotary diffusion. To begin with, we simulate so-called straight swimmers that lack intrinsic orientation decorrelation mechanisms, and a comparison with earlier results serves as a proof of principle. Next, we simulate suspensions of swimmers that tumble and undergo rotary diffusion, as a function of the swimmer number density (n), and the intrinsic decorrelation time (the average duration between tumbles, τ , for tumblers, and the inverse of the rotary diffusivity, D −1 r , for rotary diffusers). The simulations, as a function of the decorrelation time, are carried out with hydrodynamic interactions (between swimmers) turned off and on, and for both pushers and pullers (swimmers with contractile force dipoles). The 'interactions-off' simulations allow for a validation based on analytical expressions for the tracer diffusivity in the stable regime, and reveal a non-trivial box size dependence that arises with varying strength of the hydrodynamic interactions. The 'interactions-on' simulations lead us to our main finding: the existence of a box-size-independent parameter that characterizes the onset of instability in a pusher suspension, and is given by nUL 2 τ for tumblers and † Email address for correspondence: sganesh@jncasr.ac.in ‡ Present address:Collective motion in micro-swimmer suspensions 423 nUL 2 /D r for rotary diffusers; here, U and L are the swimming speed and swimmer length, respectively. The instability manifests as a bifurcation of the tracer diffusivity curves, in pusher and puller suspensions, for values of the above dimensionless parameters exceeding a critical threshold.

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“…CW intervals, on average, are longer than CCW intervals. Since the forward and backward free swimming speeds are roughly equal [3], greater CW bias results in greater displacements during forward swimming.…”

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confidence: 99%

Flagellar Motor Switching inCaulobacter CrescentusObeys First Passage Time Statistics

Morse

Bell

et al. 2015

Phys. Rev. Lett.

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Helical motion of the cell body enhances Caulobacter crescentus motility

Cited by 81 publications

References 20 publications

Buckling Instabilities and Complex Trajectories in a Simple Model of Uniflagellar Bacteria

Buckling Instabilities and Complex Trajectories in a Simple Model of Uniflagellar Bacteria

Collective motion in a suspension of micro-swimmers that run-and-tumble and rotary diffuse

Flagellar Motor Switching inCaulobacter CrescentusObeys First Passage Time Statistics

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