Pyrocystis noctiluca represents an excellent bioassay for demonstration of shear forces induced in ground-based microgravity simulators

Abstract

Ground-based facilities, such as clinostats and random positioning machines aim to simulate microgravity conditions in order to prepare space experiments and identify gravity-related signaling pathways. However, they have to be operated in an appropriate manner and potentially induced side-effects, such as shearing forces, have to be taken into account. Dinoflagellates, such as P. noctiluca, are fast and sensitive reporter systems for shear stress and hydrodynamic gradients. Deformation of the cell membrane of P. noctiluca due to shear stress results in a detectable bioluminescence emission. We exposed them Random Positioning Machine (Dutch office of Airbus), operated either as a 2D clinostat mode (constant rotation around one axis, 60 rpm) or in a 3D random mode, that means rotating around two axes, whose velocity and direction were chosen at random. Results: Our results show that the amount of mechanical stress is higher on an RPM machine than during constant clinorotation, as indicated by the differences in photon counts. We conclude that one axis clinorotation induced negligible small side effects in the form of shear forces in contrast to random operation modes tested. Conclusions: Ground-based facilities provide the opportunity to prepare space experiments and learn about the sensitivity and behavior of the biological system of interest. However, operation modes should be carefully considered in order to avoid misinterpretation of results impacted by external forces resulting in stress response.