Polarotaxis, gravitaxis and vertical phototaxis in the green flagellate, Euglena gracilis

Abstract

A fully automatic computer-controlled video analysis system has been used to study the movement of the green unicellular flagellate, Euglena gracilis in a horizontal or vertical cuvette. In darkness, in the absence of gaseous gradients, most cells swim straight upwards. While in a horizontal cuvette the transition between positive and negative phototaxis is found at about 1.5 W m-2, an excess of 30 W m-2 is required to reverse the upward swimming (due to the combined stimulus of negative gravitaxis and positive phototaxis) in a vertical cuvette. By studying the swimming direction in horizontal and vertical cuvettes in polarized light irradiated from above or from the side, respectively, the dichroic orientation of the photoreceptor molecules can be determined in three dimensions with respect to the axes of the cell; In a horizontal cuvette, in a linearly polarized beam from above, the cells orient predominantly at an angle of about 30 degrees clockwise off the electric dipole transition moment as seen from above. The behavior in a vertical cuvette with polarized light entering from above indicates that the photoreceptor pigments are dichroically oriented 60 degrees counterclockwise from the flagellar plane (seen from the front end of the cell). Experiments with horizontal polarized light indicate that the photoreceptor transition moment deviates 25 degrees clockwise off the long axis of the cell.

Influence of Different Light-Dark Cycles on Motility and Photosynthesis ofEuglena gracilisin Closed Bioreactors

“…This organism is believed to have a high potential as an oxygen producer in biological lifesupport systems either alone or in combination with higher plants. The cells show an interesting movement behavior toward light, gravity, and oxygen (Häder, 1987;Porterfield, 1997). In darkness, the cells swim upward in the water column, which is referred to as negative gravitaxis.…”

An interactive programming paradigm for realtime experimentation with remote living matter

“…4). We note that such an experiment is realistic, as similar experiments have been published in microbiology and biophysics journals [7,8,16].…”

A new interpretation of the Keller-Segel model based on multiphase modelling

“…For example, we could distinguish between cells that move by crawling over a substrate [8,9] and organisms that swim by beating their flagella [9,26,27]. In order to describe cell crawling it would be necessary to introduce a third phase for the ex- Other model modifications for which there is strong experimental evidence include assuming that the cell proliferation and death terms depend on the stress that the cells experience [14].…”

“…Obviously the mechanisms that regulate the movement of different types of cells and/or simple motile organisms are cell-(or organism-) specific. For ex-ample, leukocytes migrate towards a site of infection by crawling over the underlying tissue matrix [9,11,25] whereas bacteria such as Escherichia coli swim by a combination of advection and rotation [6,9] and other bacteria such as Euglena gracilis swim towards a light-source by beating their flagella in an appropriate manner [26,27]. When developing our model we have not considered the details of how the cells move: instead we have focussed on the role played by the diffusible chemical.…”