A lumped parameter model of endoplasm flow in Physarum polycephalum explains migration and polarization-induced asymmetry during the onset of locomotion

Oettmeier, Christina; Döbereiner, Jürgen

doi:10.1371/journal.pone.0215622

Cited by 21 publications

(24 citation statements)

References 42 publications

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“…The flow is always laminar, as observed in our μPIV measurements (figure 2), by Doppler optical coherence tomography [22], and particle tracking velocimetry [23]. The Womersley and maximum Reynolds numbers calculated using the values of the physical parameters measured in or known for P. polycephlaum are α ≈ 0.04 and Re max ≈ 0.27, in good agreement with values obtained in narrower veins of P. polycephalum [24,44]. The low Womersley and oscillatory Reynolds numbers corroborate that the flow is laminar at all times.…”

Section: Discussionsupporting

confidence: 86%

Effective mixing due to oscillatory laminar flow in tubular networks of plasmodial slime moulds

Haupt

Hauser

2020

New J. Phys.

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The plasmodium of the unicellular slime mould Physarum polycephalum forms an extended vascular network in which protoplasm is transported through the giant cell due to peristaltic pumping. The flow in the veins is always parabolic and it performs shuttle streaming, i.e., the flow reverses its direction periodically. However, particles suspended in the protoplasm are effectively and rapidly distributed within the cell. To elucidate how an effective mixing can be achieved in such a microfluidic system with Poiseuille flow, we performed micro-particle imaging velocimetry experiments and advected virtual tracers in the determined time-dependent flow fields. Two factors were found to be crucial for effective mixing: (i) flow splitting and flow reversals occurring at junctions of veins and (ii) small delays in the reversals of flows in the veins at a junction. These factors enhance the distribution of fluid volumes and hence promote mixing due to chaotic advection. From the residence time distributions of particles at a junction, it is estimated that about 10% of the volume is effectively redistributed at a junction during one period of the shuttle streaming. We presume that the principles of mixing unravelled in P. polycephalum represent a promising approach to achieve efficient mixing in man-made microfluidic devices. Figure 1. Network of tubular veins in the plasmodium of P. polycephalum strand HU195 × HU200. The cell extends and propagates to the right. The dense apical front (at the right) gives way to a vast network of tubular stands, where protoplasm is transported by peristalsis. Dimensions: 6.14 × 4.60 cm 2 .can be adapted to the situation in P. polycephalum. By contrast to linear veins, in branched hemo-dynamic flow networks, there are feedbacks between the local pressures generated by the contraction of the veins, the flow velocity of protoplasm, and the compliance of the veins (i.e., the increase in their diameter) [11]. This leads to phase shifts between the flows that emanate from (and lead to) a junction of veins.Several models have been put forward to describe the interplay between the cellular mechanics of the vein and the peristaltic flow [8,12,13]. These models all rely on a coupling between the underlying biochemical (driving) system, that is coupled to cell and fluid mechanics. These models have sparked a novel interest in studying the mechanical properties of P. polycephalum [14].The vein network of P. polycephalum forms regular graphs, i.e., graphs with a unique node degree k = 3 [1, 2]. The vein segments have different thicknesses and lengths [1,2] in order to provide for an optimized transport of protoplasm through the cell [15,16]. With respect to transport efficiency, the architecture of these networks is hierarchic and self-similar [16]. Furthermore, the networks are highly adaptive [1,2,15], and an originally dense network may coarsen with time [1,2,[15][16][17][18]. In the absence of any external cue, the contraction of the thicker veins is almost synchronous over the entire network [19], ...

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Section: Discussionsupporting

confidence: 86%

Effective mixing due to oscillatory laminar flow in tubular networks of plasmodial slime moulds

Haupt

Hauser

2020

New J. Phys.

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“…Much larger forms of Physarum like mesoplasmodia and extended networks show a clear separation of gel and fluid-like phases [8, 12, 63, 64]. Recently, a study by Weber et.…”

Section: Discussionmentioning

confidence: 99%

Active poroelastic two-phase model for the motion of physarum microplasmodia

et al. 2019

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The onset of self-organized motion is studied in a poroelastic two-phase model with free boundaries for Physarum microplasmodia (MP). In the model, an active gel phase is assumed to be interpenetrated by a passive fluid phase on small length scales. A feedback loop between calcium kinetics, mechanical deformations, and induced fluid flow gives rise to pattern formation and the establishment of an axis of polarity. Altogether, we find that the calcium kinetics that breaks the conservation of the total calcium concentration in the model and a nonlinear friction between MP and substrate are both necessary ingredients to obtain an oscillatory movement with net motion of the MP. By numerical simulations in one spatial dimension, we find two different types of oscillations with net motion as well as modes with time-periodic or irregular switching of the axis of polarity. The more frequent type of net motion is characterized by mechano-chemical waves traveling from the front towards the rear. The second type is characterized by mechano-chemical waves that appear alternating from the front and the back. While both types exhibit oscillatory forward and backward movement with net motion in each cycle, the trajectory and gel flow pattern of the second type are also similar to recent experimental measurements of peristaltic MP motion. We found moving MPs in extended regions of experimentally accessible parameters, such as length, period and substrate friction strength. Simulations of the model show that the net speed increases with the length, provided that MPs are longer than a critical length of ≈ 120 μm. Both predictions are in line with recent experimental observations.

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“…For instance, while existing mathematical models can predict how changing specific parameters (e.g., substrate friction or ectoplasm shear modulus) affects detailed observable variables (e.g., membrane shape or substrate traction stress), the existing experimental data have been until recently mostly limited to measurements of cell thickness over time in round static microplasmodia. Experimental studies of Physarum microplasmodial locomotion have become increasingly common in recent years [16,[18][19][20][21], but symmetry breaking has comparatively received little attention.…”

Section: Introductionmentioning

confidence: 99%

Symmetry breaking transition towards directional locomotion inPhysarummicroplasmodia

Zhang¹,

Lasheras²,

Álamo³

2019

J. Phys. D: Appl. Phys.

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True slime mold Physarum polycephalum has been widely used as a model organism to study flow-driven amoeboid locomotion as well as the dynamics of its complex mechanochemical self-oscillations. The aim of this work is to quantify the mechanical aspects of symmetry breaking and its transition into directional flow-driven amoeboid locomotion in small (<∼ 200 µm) fragments of Physarum polycephalum. To this end, we combined measurements of traction stresses, fragment morphology, and ectoplasmic microrheology with experimental manipulations of cell-substrate adhesion, cortical strength and microplasmodium size. These measurements show that initiation of locomotion is accompanied by the symmetry breaking of traction stresses and the polarization of ectoplasmic mechanical properties, with the rear part of the microplasmodium becoming significantly stiffer after the onset of locomotion. Our experimental data suggests that the initiation of locomotion in Physarum could be analogous to an interfacial instability process and that microplasmodial size is a critical parameter governing the instability. Specifically, our results indicate that the instability driving the onset of locomotion is strengthened by substrate adhesiveness and weakened by cortical stiffness. Furthermore, the Fourier spectral analysis of morphology revealed lobe number n = 2 as the consistent dominant mode number across various experimental manipulations, suggesting that the instability mechanism driving the onset of Physarum locomotion is robust with respect to changes in environmental conditions and microplasmodial properties.

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A lumped parameter model of endoplasm flow in Physarum polycephalum explains migration and polarization-induced asymmetry during the onset of locomotion

Cited by 21 publications

References 42 publications

Effective mixing due to oscillatory laminar flow in tubular networks of plasmodial slime moulds

Effective mixing due to oscillatory laminar flow in tubular networks of plasmodial slime moulds

Active poroelastic two-phase model for the motion of physarum microplasmodia

Symmetry breaking transition towards directional locomotion inPhysarummicroplasmodia

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