Machemer H, Bräucker R, Takahashi K, Murakami A (1993): Graviperception in unicellular organisms: a comparative behavioural study under short-term microgravity

Three species of unicellular ciliated organisms, Paramecium, Didinium and Loxodes, were adjusted to defined culturing state, experimental solution, O2-supply and temperature and subjected to step-type transition from terrestrial gravity to 4.5 seconds of microgravity (near 10-4g) in a drop tower. For a quantitative approach to cellular behaviour under microgravity, four identical modules designed for video-tape recording of cellular locomotion (velocity, orientation) were incubated at one time in the drop capsule, and each module held an experimental chamber including 100 to 200 cells. Image analysis of the data shows that the normal orientational bias of vertically swimming cells of Paramecium and Didinium(negative gravitaxis) was missing under microgravity; so were gravity-induced changes in velocity of these cells (gravikinesis), which tend to compensate passive sedimentation rates at 1g. The rates of µg-locomotion in Paramecium and Loxodes correspond to horizontal locomotion at 1g. In Didinium, swimming at µg exceeds horizontal swimming at 1g. These data are interpreted in terms of the mechanosensory organization of these cells and of a previously published model of electrophysiologically regulated gravisensory transduction.