Preferred negative geotactic orientation in mobile cells: Tetrahymena results

Abstract

For the protozoan species Tetrahymena a series of airplane experiments are reported, which varied gravity as an active laboratory parameter and tested for corresponding changes in geotaxic orientation of single cells. The airplane achieved alternating periods of low (0.01 g) and high (1.8 g; g = 980 cm/s) gravity by flying repeated Keplerian parabolas. The experimental design was undertaken to clearly distinguish gravity from competing aerodynamic and chemical gradients. In this way, each culture served as its own control, with gravity level alone determining the orientational changes. On average, 6.3% of the Tetrahymena oriented vertically in low gravity, while 27% oriented vertically in high-gravity phases. Simplified physical models are explored for describing these cell trajectories as a function of gravity, aerodynamic drag, and lift. The notable effect of gravity on turning behavior is emphasized as the biophysical cause of the observed negative geotaxis in Tetrahymena. A fundamental investigation of the biological gravity receptor (if it exists) and improved modeling for vertical migration in important types of ocean plankton motivate the present research.

Entrapment of Ciliates at the Water-Air Interface

“…It is known that Tetrahymena show both aerotaxis and geotaxis [15], [16]. Thus, cells naturally tend to swim upwards, i.e.…”

Some but not All Tetrahymena Species Destroy Monolayer Cultures of Cells from a Wide Range of Tissues and Species

“…Negative geotaxis has previously been described in T. pyriformis (Noever et al. ), and because of the low volume of medium, other explanations for directed movement of the ciliates, namely dissolved oxygen, chemical, or light gradients, are not expected to have been a major factor. Detailed study of the physiology of T. canadensis has yet to be carried out.…”

“…Another explanation may be geotaxis, whereby movement of the cell is directed by gravity, specifically T. canadensis may exhibit negative geotaxis and swim upwards in the culture vessel. Negative geotaxis has previously been described in T. pyriformis (Noever et al 1994), and because of the low volume of medium, other explanations for directed movement of the ciliates, namely dissolved oxygen, chemical, or light gradients, are not expected to have been a major factor. Detailed study of the physiology of T. canadensis has yet to be carried out.…”

Ingestion without Inactivation of Bacteriophages by Tetrahymena

“…Protistophoresis might also be significant in preventing phages from being lost from soil by the downward drainage of rainwater. Many protists, including Tetrahymena , exhibit negative gravitaxis (Kowalewski, Braeuker, and Machemer 1998; Noever, Crinise, and Matsos 1994) and positive oxytaxis or aerotaxis (Shvirst, Krinskii, and Ivanitskii 1984). Ingested phages, due to upward transport, would tend to remain in the protist‐ and bacteria‐rich soil surface layer (Fierer, Schimel, and Holden 2003).…”