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Simple dynamics underlying the survival behaviors of ciliates - PubMed

  • ️Sat Jan 01 2022

Simple dynamics underlying the survival behaviors of ciliates

Takuya Ohmura et al. Biophys Physicobiol. 2022.

Abstract

Ciliates are swimming microorganisms in aquatic environments. Habitats where ciliates accumulate include nutrient-rich solid-liquid interfaces such as pond bottom walls and waterweed surfaces. The ciliates stay near the walls to survive. We investigated the dynamics of the near-wall behavior of ciliates. In experiments, the ciliates were made to slide on a flat wall of glass substrate. When encountering the wall, the wall-side cilia of the cells stop their motion and lose their propelling activity, which indicates that the ciliates have a mechano-sensing system for cilia beating. Based on the experimental results, we hypothesized that the ciliary thrust force that propels the cell body becomes asymmetric, and the asymmetry of the thrust force generates a head-down torque to keep the cell sliding on the wall. To prove this hypothesis, we performed numerical simulations by using a developed hydrodynamic model for swimming ciliates. The model revealed that the loss of cilia activity on the wall side physically induces a sliding motion, and the aspect ratio of the cell body and effective cilium area are critical functions for the sliding behavior on a wall. In addition, we investigated the stability of the sliding motion against an external flow. We found that ciliates slide upstream on a wall. Interestingly, the dynamics of this upstream sliding, called rheotaxis, were also explained by the identical physical conditions for no-flow sliding. Only two simple physical conditions are required to explain the dynamics of ciliate survival behavior. This review article is an extended version of the Japanese article, Fluid Dynamic Model Reveals a Mechano-sensing System Underlying the Behavior of Ciliates, published in SEIBUTSU BUTSURI Vol. 61, p. 16-19 (2021).

Keywords: fluid dynamics; mechano-sensing; rheotaxis; sliding motion; swimming microorganism.

2022 THE BIOPHYSICAL SOCIETY OF JAPAN.

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Figures

Figure 1
Figure 1

Snapshot of T. pyriformis sliding on a glass surface. Scale bar is 20 μm.

Figure 2
Figure 2

Schematics of cell swimming patterns. Top and bottom row represent actual cells and hydrodynamic models, respectively [41].

Figure 3
Figure 3

Observations of sliding ciliates. A: Snapshots of sliding T. pyriformis. B: Snapshots of sliding P. caudatum. C: Multilayered visualized cilia. D: Schematic illustration of thrust force around ciliates encountering a wall [41].

Figure 4
Figure 4

Numerical simulation setup and results [41].

Figure 5
Figure 5

Schematics of torques involved in a ciliary swimmer contacting a wall [41].

Figure 6
Figure 6

Diagram of reactive motions of a ciliary swimmer [41].

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