Gravikinesis in Paramecium: Approach from the analysis on the swimming behavior of single cells

Abstract

Gravitaxis of swimming microorganisms has so far been explained largely in terms of the physical properties of the microorganisms that are assumed not to have any speculative mechanisms of gravity sensation. However gravity-induced sensory input and the subsequent modulation of locomotor activity in Paramecium has been suggested by precise analyses of swimming velocity as a function of swimming direction with respect to gravity. Paramecium appears to modulate its propulsive effort depending on the swimming direction by increasing the propulsive speed in upward and decreasing it in downward directions. This response termed as gravikinesis was obtained from the averaged measurement on a large number of the cell. In the present study we aimed to confirm the results on the basis of the measurement on the swimming of a single cell. Velocities of upward and downward swimming was measured from each single cell, and the velocity of sinking was measured on the same cell which was immobilized by Ni 2+. We confirmed the gravikinesis from the analysis on the swimming of single cells. In addition, we found that in the hyper-density medium containing Percoll cells showed opposite gravikinesis to that in the hypo-density medium. These results may suggest the mechanosensitivity of the cell membrane as a physiological sensor underlying the gravity-dependent response in Paramecium.

Deformation of a micro-torque swimmer

“…These results indicate that the overall swimming velocity was approximately the superposition of the sedimentation velocity and the swimming velocity without a gravity effect. In reality, however, the difference between the upward and downward swimming velocities of Paramecium was much less than the superimposed value [ 4 – 6 ]. The inconsistency of the present results clearly illustrates that some biological responses to the gravity field should be introduced to explain the experimental observations.…”

“…These observations suggest that the swimming velocity in the vertically upward direction may become about nine body lengths per second, whereas that in the vertically downward direction may become about 11 body lengths per second due to the sedimentation effect. Some researchers have actually measured the upward and downward swimming velocities of Paramecium [ 4 – 6 ]. Surprisingly, the difference between the upward and downward swimming velocities was much less than the expected value, and the sedimentation effect was considerably reduced.…”

Gravitactic Swimming of the Planula Larva of the Coral Acropora: Characterization of Straightforward Vertical Swimming

“…For the viscosity-dominant motion under the influence of gravity, swimming velocity is determined by the vector sum of the active propulsive velocity and passive sedimentation velocity (Machemer et al, 1991;Ooya et al, 1992;Takeda et al, 2006). Therefore, in the case of vertical swimming of planulae,…”

Bioconvective Linear Stability of Gravitactic Microorganisms

“…[40][41][42] about the pattern formation in suspensions of Tetrahymena and Chlamydomonas subject to different gravity conditions. Further results are due to Sawai et al [43] who investigate the proliferation of Paramecium under simulated microgravity, to Mogami et al [44] who report an investigation of the formed patterns by Tetrahymena and Chlamydomonas as well as a physiological comparison, to Takeda et al [45] who give an explanation of the gravitactic behavior of single cells of Paramecium in terms of the swimming velocity and swimming direction, to Mogami et al [46] who present theory and experiments of two mechanisms of gravitactic behavior for microorganisms, and to Itoh et al [47] who investigate the modification of bioconvective patterns under strong gravitational fields.…”