Pyrocystis noctiluca represents an excellent bioassay for shear forces induced in ground-based microgravity simulators (clinostat and random positioning machine)

Abstract

Ground-based facilities, such as clinostats and random positioning machines aiming at simulating microgravity conditions, are tools to prepare space experiments and identify gravity-related signaling pathways. A prerequisite is that the facilities are operated in an appropriate manner and potentially induced non-gravitational effects, such as shearing forces, have to be taken into account. Dinoflagellates, here P. noctiluca, as fast and sensitive reporter system for shear stress and hydrodynamic gradients, were exposed on a clinostat (constant rotation around one axis, 60 rpm) or in a random positioning machine, that means rotating around two axes, whose velocity and direction were chosen at random. Deformation of the cell membrane of P. noctiluca due to shear stress results in a detectable bioluminescence emission. Our results show that the amount of mechanical stress is higher on an random positioning machine than during constant clinorotation, as revealed by the differences in photon counts. We conclude that one axis clinorotation induced negligible non-gravitational effects in the form of shear forces in contrast to random operation modes tested. For the first time, we clearly visualized the device-dependent occurrence of shear forces by means of a bioassay, which have to be considered during the definition of an appropriate simulation approach and to avoid misinterpretation of results.

Validation of Random Positioning Versus Clinorotation Using a Macrophage Model System

“…Even more, since recent studies point out that random positioning results in the induction of fluid shear forces, which may affect the exposed cells and mask gravity-related effects (Wüest et al 2015(Wüest et al , 2017. Using the dinoflagellate Pyrocystis noctiluca and its capacity to act as bioassay for mechanical stress, Hauslage and coworkers visualized the shear forces induced by random positioning in contrast to clinorotation (Hauslage et al 2017).…”

Analysis of Statoliths Displacement in Chara Rhizoids for Validating the Microgravity-Simulation Quality of Clinorotation Modes

“…Bioluminescence is part of the defense mechanism of these dinoflagellates. The combination of random speed and direction of the PRM had a stronger impact on bioluminescence of the dinoflagellate Dinocystis noctiluca than only changing the rotational speed or using a fast and constantly rotating clinostat at 60 rpm (Hauslage et al 2017) clearly indicating a higher stress level caused by the 3D operation mode.…”

“…When the RPM is operated in the real-random mode, microgravity simulation is characterized by a constantly changing rotation velocity and in addition also a constantly changing direction of rotation. Clear evidence for the negative impact of the real-random mode on cellular activities comes from experiments with the fast and sensitive shear stress reporter system of dinoflagellates (Hauslage et al 2017). Shear stress and hydrodynamic gradients trigger a luciferin/luciferase reaction in dinoflagellates probably via a calcium mediated signaling cascade (Mallipattu et al 2002;Jin et al 2013;Von Dassow and Latz 2002).…”

Guanylyl Cyclase-cGMP Signaling Pathway in Melanocytes: Differential Effects of Altered Gravity in Non-Metastatic and Metastatic Cells

“…Comparative studies between the different simulation approaches are necessary to understand what is really achieved for the exposed systems [68,69]. For example, exposure of a fast biosensor of mechanical stress-the dinoflagellate Pyrocystis noctiluca-visualized the shear forces induced by random positioning in contrast to clinorotation [70,71]. It is therefore recommended to perform comparative studies due to the different working principles of the RPM and the clinostat.…”