Swimming Paramecium in magnetically simulated enhanced, reduced, and inverted gravity environments

Abstract

Earth's gravity exerts relatively weak forces in the range of 10 -100 pN directly on cells in biological systems. Nevertheless, it biases the orientation of swimming unicellular organisms, alters bone cell differentiation, and modifies gene expression in renal cells. A number of methods of simulating different strength gravity environments, such as centrifugation, have been applied for researching the underlying mechanisms. Here, we demonstrate a magnetic force-based technique that is unique in its capability to enhance, reduce, and even invert the effective buoyancy of cells and thus simulate hypergravity, hypogravity, and inverted gravity environments. We apply it to Paramecium caudatum, a single-cell protozoan that varies its swimming propulsion depending on its orientation with respect to gravity, g. In these simulated gravities, denoted by f gm, Paramecium exhibits a linear response up to fgm ‫؍‬ 5 g, modifying its swimming as it would in the hypergravity of a centrifuge. Moreover, experiments from f gm ‫؍‬ 0 to ؊5 g show that the response is symmetric, implying that the regulation of the swimming speed is primarily related to the buoyancy of the cell. The response becomes nonlinear for f gm >5 g. At fgm ‫؍‬ 10 g, many paramecia ''stall'' (i.e., swim in place against the force), exerting a maximum propulsion force estimated to be 0.7 nN. These findings establish a general technique for applying continuously variable forces to cells or cell populations suitable for exploring their force transduction mechanisms.buoyancy ͉ force ͉ gravikinesis ͉ levitation ͉ microorganism

Hydrodynamic sensing and behavior by oyster larvae in turbulence and waves

“…This estimate is ∼10 3 times lower than the maximum power output for oyster larvae (Fig. 10I,J), but the difference is reasonable given that oyster larvae are negatively buoyant and must use more propulsive force to counteract requires ≥100 times more propulsive force in oyster larvae than in Paramecia (Sleigh and Blake, 1977;Guevorkian and Valles, 2006;Fig. 10).…”

Ground-Based Facilities for Simulation of Microgravity: Organism-Specific Recommendations for Their Use, and Recommended Terminology

“…These were followed by studies of levitating yeast (Coleman et al, 2007), swimming paramecia in gadolinium solution (Guevorkian and Valles, 2006b), E. coli (Dijkstra et al, 2011), cell cultures (Babbick et al, 2007;Hammer et al, 2009;Qian et al, 2009), a mouse , and Drosophila melanogaster Hill et al, 2012).…”

The mechanics of gravitaxis inParamecium

“…The situation may be compared with that of an oarsman in a rowing boat being pulled along by a rope affixed to the bow, who can exert no additional forward propulsive force with his oar if the water is rushing back past him faster than the backward swing velocity of his blade. This is a possible explanation for the observation that an eightfold increase in the sedimentary flow reduces the propulsive force in down-swimming P. caudatum to zero while similarly augmenting up-swimming velocities (Guevorkian and Valles, 2006). Both these mechanisms could potentially contribute to gravikinesis in Paramecium.…”

“…However, it may be remarked that gravikinesis does not seem to confer much benefit on the organism. Net upward migration in a randomly moving population of organisms produced by gravikinesis alone can only be achieved if /S>2, where  is the magnitude of the gravikinetic increment in swimming velocity under normal gravity and S is the average sedimentation rate, whereas reported values of /S in Paramecium are only around 0.6 (Bräucker et al, 1994;Nagel and Machemer, 2000;Guevorkian and Valles, 2006). Increased reversal rates in down-swimming cells could also produce a net upward drift, but ciliary reversal frequencies are extremely low in adapted cultures (Nagel and Machemer, 2000) and are unlikely to have a significant effect.…”